bpo-35976: Enable Windows projects to build with platform ARM32 (GH-11825)

This change adds the necessary items to the build projects to avoid erroring out right at the start. It does not add _support_ for targeting Windows on ARM32, but is a necessary prerequisite for adding it.
diff --git a/PCbuild/_decimal.vcxproj b/PCbuild/_decimal.vcxproj
index df9f600..fa4bb8d 100644
--- a/PCbuild/_decimal.vcxproj
+++ b/PCbuild/_decimal.vcxproj
@@ -1,6 +1,10 @@
 <?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|ARM">
+      <Configuration>Debug</Configuration>
+      <Platform>ARM</Platform>
+    </ProjectConfiguration>
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
       <Platform>Win32</Platform>
@@ -9,6 +13,10 @@
       <Configuration>Debug</Configuration>
       <Platform>x64</Platform>
     </ProjectConfiguration>
+    <ProjectConfiguration Include="PGInstrument|ARM">
+      <Configuration>PGInstrument</Configuration>
+      <Platform>ARM</Platform>
+    </ProjectConfiguration>
     <ProjectConfiguration Include="PGInstrument|Win32">
       <Configuration>PGInstrument</Configuration>
       <Platform>Win32</Platform>
@@ -17,6 +25,10 @@
       <Configuration>PGInstrument</Configuration>
       <Platform>x64</Platform>
     </ProjectConfiguration>
+    <ProjectConfiguration Include="PGUpdate|ARM">
+      <Configuration>PGUpdate</Configuration>
+      <Platform>ARM</Platform>
+    </ProjectConfiguration>
     <ProjectConfiguration Include="PGUpdate|Win32">
       <Configuration>PGUpdate</Configuration>
       <Platform>Win32</Platform>
@@ -25,6 +37,10 @@
       <Configuration>PGUpdate</Configuration>
       <Platform>x64</Platform>
     </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|ARM">
+      <Configuration>Release</Configuration>
+      <Platform>ARM</Platform>
+    </ProjectConfiguration>
     <ProjectConfiguration Include="Release|Win32">
       <Configuration>Release</Configuration>
       <Platform>Win32</Platform>
@@ -63,6 +79,7 @@
     <ClCompile>
       <PreprocessorDefinitions>_CRT_SECURE_NO_WARNINGS;MASM;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <PreprocessorDefinitions Condition="'$(Platform)' == 'Win32'">CONFIG_32;PPRO;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions Condition="'$(Platform)'=='ARM'">CONFIG_32;ANSI;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <PreprocessorDefinitions Condition="'$(Platform)' == 'x64'">CONFIG_64;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>..\Modules\_decimal;..\Modules\_decimal\libmpdec;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
     </ClCompile>
@@ -106,6 +123,7 @@
   <ItemGroup>
     <CustomBuild Include="..\Modules\_decimal\libmpdec\vcdiv64.asm">
       <ExcludedFromBuild Condition="'$(Platform)'=='Win32'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Platform)'=='ARM'">true</ExcludedFromBuild>
       <Command>ml64 /nologo /c /Zi /Fo "$(IntDir)vcdiv64.obj" "%(FullPath)"</Command>
       <Outputs>$(IntDir)vcdiv64.obj;%(Outputs)</Outputs>
     </CustomBuild>