pythongh-110437: Allow overriding VCRuntimeDLL with a semicolon separated list of DLLs to bundle (pythonGH-110470)

(cherry picked from commit 12cc679)

Co-authored-by: Steve Dower <steve.dower@python.org>

Author: zooba

Misc/NEWS.d/next/Windows/2023-10-06-14-20-14.gh-issue-110437.xpYy9q.rst

@@ -0,0 +1,2 @@
+Allows overriding the source of VC redistributables so that releases can be
+guaranteed to never downgrade between updates.

PCbuild/pyproject.props

@@ -232,7 +232,10 @@ public override bool Execute() {
   </Target>
 
   <Target Name="FindVCRuntime" Returns="VCRuntimeDLL" DependsOnTargets="FindVCRedistDir">
-    <ItemGroup Condition="$(VCInstallDir) != ''">
+    <ItemGroup Condition="$(VCRuntimeDLL) != ''">
+      <VCRuntimeDLL Include="$(VCRuntimeDLL)" />
+    </ItemGroup>
+    <ItemGroup Condition="$(VCInstallDir) != '' and $(VCRuntimeDLL) == ''">
       <VCRuntimeDLL Include="$(VCRedistDir)\Microsoft.VC*.CRT\vcruntime*.dll" />
     </ItemGroup>