Issue #15968: Incorporated Tcl, Tk, and Tix builds into the Windows build
solution.

Currently, Tix is not built in Debug configuration.

This change also:
- simplifies some Tcl/Tk-related msbuild properties for _tkinter
- copies the Tcl and Tk DLLs into the build output directory, meaning
  they will always be available after a build without having to copy
  them manually or change PATH
- removes PCbuild/build_tkinter.py: the solution does the build without
  needing to invoke Python (so Tcl/Tk/Tix can be built in parallel with
  the rest of the build using the `/m` msbuild command line switch)
- removes an outdated README concerning building Tcl/Tk on AMD64
diff --git a/PCbuild/tix.vcxproj b/PCbuild/tix.vcxproj
new file mode 100644
index 0000000..a177f5c
--- /dev/null
+++ b/PCbuild/tix.vcxproj
@@ -0,0 +1,171 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGInstrument|Win32">
+      <Configuration>PGInstrument</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGInstrument|x64">
+      <Configuration>PGInstrument</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGUpdate|Win32">
+      <Configuration>PGUpdate</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGUpdate|x64">
+      <Configuration>PGUpdate</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}</ProjectGuid>
+    <RootNamespace>tix</RootNamespace>
+    <Keyword>MakeFileProj</Keyword>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='PGUpdate|Win32'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='PGInstrument|Win32'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='PGUpdate|x64'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='PGInstrument|x64'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="Configuration">
+    <ConfigurationType>Makefile</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='PGUpdate|Win32'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="pgupdate.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='PGInstrument|Win32'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="pginstrument.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="release.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="debug.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='PGUpdate|x64'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="x64.props" />
+    <Import Project="pgupdate.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='PGInstrument|x64'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="x64.props" />
+    <Import Project="pginstrument.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="x64.props" />
+    <Import Project="release.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+    <Import Project="x64.props" />
+    <Import Project="debug.props" />
+    <Import Project="tcltk.props" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup>
+    <_ProjectFileVersion>10.0.30319.1</_ProjectFileVersion>
+    <NMakeBuildCommandLine>
+IF EXIST $(tcltkDir)\lib\tix8.4.3\$(tixDLLName) (
+    echo Tix is already built and available.
+    exit /b 0
+)
+
+IF NOT EXIST $(tixDir) (
+    echo error: $(tixDir) doesn't exist.
+    exit 1
+)
+
+IF "$(Platform)" EQU "Win32" set TclMachine=IX86
+IF "$(Platform)" EQU "x64" set TclMachine=AMD64
+
+IF "$(Configuration)" EQU "Debug" (
+    set TixDebug=1
+) ELSE (
+    set TixDebug=0
+)
+
+cd $(tixDir)\win
+nmake -f python.mak MACHINE=%TclMachine% DEBUG=%TixDebug% TCL_DIR=$(SolutionDir)$(tclDir) TK_DIR=$(SolutionDir)$(tkDir) all &amp;&amp; nmake -f python.mak MACHINE=%TclMachine% DEBUG=%TixDebug% TCL_DIR=$(SolutionDir)$(tclDir) TK_DIR=$(SolutionDir)$(tkDir) INSTALL_DIR=$(SolutionDir)$(tcltkDir) install
+    </NMakeBuildCommandLine>
+    <NMakeCleanCommandLine>echo Tix must be cleaned manually if you want to rebuild it.</NMakeCleanCommandLine>
+  </PropertyGroup>
+  <ItemDefinitionGroup>
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ProjectReference Include="tcl.vcxproj">
+      <Project>{b5fd6f1d-129e-4bff-9340-03606fac7283}</Project>
+    </ProjectReference>
+    <ProjectReference Include="tk.vcxproj">
+      <Project>{7e85eccf-a72c-4da4-9e52-884508e80ba1}</Project>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  </ImportGroup>
+</Project>
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