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- removes an outdated README concerning building Tcl/Tk on AMD64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/pcbuild.sln b/PCbuild/pcbuild.sln
index a346e10..78f403e 100644
--- a/PCbuild/pcbuild.sln
+++ b/PCbuild/pcbuild.sln
@@ -78,6 +78,12 @@
 EndProject

 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "_testembed", "_testembed.vcxproj", "{6DAC66D9-E703-4624-BE03-49112AB5AA62}"

 EndProject

+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "tcl", "tcl.vcxproj", "{B5FD6F1D-129E-4BFF-9340-03606FAC7283}"

+EndProject

+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "tk", "tk.vcxproj", "{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}"

+EndProject

+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "tix", "tix.vcxproj", "{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}"

+EndProject

 Global

 	GlobalSection(SolutionConfigurationPlatforms) = preSolution

 		Debug|Win32 = Debug|Win32

@@ -645,6 +651,52 @@
 		{6DAC66D9-E703-4624-BE03-49112AB5AA62}.Release|Win32.Build.0 = Release|Win32

 		{6DAC66D9-E703-4624-BE03-49112AB5AA62}.Release|x64.ActiveCfg = Release|x64

 		{6DAC66D9-E703-4624-BE03-49112AB5AA62}.Release|x64.Build.0 = Release|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Debug|Win32.ActiveCfg = Debug|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Debug|Win32.Build.0 = Debug|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Debug|x64.ActiveCfg = Debug|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Debug|x64.Build.0 = Debug|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGInstrument|Win32.ActiveCfg = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGInstrument|Win32.Build.0 = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGInstrument|x64.ActiveCfg = PGInstrument|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGInstrument|x64.Build.0 = PGInstrument|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGUpdate|Win32.ActiveCfg = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGUpdate|Win32.Build.0 = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGUpdate|x64.ActiveCfg = PGUpdate|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.PGUpdate|x64.Build.0 = PGUpdate|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Release|Win32.ActiveCfg = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Release|Win32.Build.0 = Release|Win32

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Release|x64.ActiveCfg = Release|x64

+		{B5FD6F1D-129E-4BFF-9340-03606FAC7283}.Release|x64.Build.0 = Release|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Debug|Win32.ActiveCfg = Debug|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Debug|Win32.Build.0 = Debug|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Debug|x64.ActiveCfg = Debug|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Debug|x64.Build.0 = Debug|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGInstrument|Win32.ActiveCfg = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGInstrument|Win32.Build.0 = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGInstrument|x64.ActiveCfg = PGInstrument|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGInstrument|x64.Build.0 = PGInstrument|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGUpdate|Win32.ActiveCfg = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGUpdate|Win32.Build.0 = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGUpdate|x64.ActiveCfg = PGUpdate|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.PGUpdate|x64.Build.0 = PGUpdate|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Release|Win32.ActiveCfg = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Release|Win32.Build.0 = Release|Win32

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Release|x64.ActiveCfg = Release|x64

+		{7E85ECCF-A72C-4DA4-9E52-884508E80BA1}.Release|x64.Build.0 = Release|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Debug|Win32.ActiveCfg = Debug|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Debug|x64.ActiveCfg = Debug|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGInstrument|Win32.ActiveCfg = PGInstrument|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGInstrument|Win32.Build.0 = PGInstrument|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGInstrument|x64.ActiveCfg = PGInstrument|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGInstrument|x64.Build.0 = PGInstrument|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGUpdate|Win32.ActiveCfg = PGUpdate|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGUpdate|Win32.Build.0 = PGUpdate|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGUpdate|x64.ActiveCfg = PGUpdate|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.PGUpdate|x64.Build.0 = PGUpdate|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Release|Win32.ActiveCfg = Release|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Release|Win32.Build.0 = Release|Win32

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Release|x64.ActiveCfg = Release|x64

+		{C5A3E7FB-9695-4B2E-960B-1D9F43F1E555}.Release|x64.Build.0 = Release|x64

 	EndGlobalSection

 	GlobalSection(SolutionProperties) = preSolution

 		HideSolutionNode = FALSE