MSBuildCache: Allow duplicate outputs under "obj\*\vcpkg\**" (#17597)

Author: dfederm

Directory.Build.props

@@ -41,6 +41,11 @@
     -->
     <MSBuildCacheIdenticalDuplicateOutputPatterns>$(MSBuildCacheIdenticalDuplicateOutputPatterns);bin\**</MSBuildCacheIdenticalDuplicateOutputPatterns>
 
+    <!-- 
+      vcpkg is invoked for each and every vcxproj and each invocation uses the same base dir for logging, so allow these duplicate "outputs".
+    -->
+    <MSBuildCacheIdenticalDuplicateOutputPatterns>$(MSBuildCacheIdenticalDuplicateOutputPatterns);obj\*\vcpkg\**</MSBuildCacheIdenticalDuplicateOutputPatterns>
+
     <!-- version of MSBuildCache is not part of the cache key -->
     <PackagesConfigFile>$(MSBuildThisFileDirectory)\dep\nuget\packages.config</PackagesConfigFile>
     <MSBuildCacheIgnoredInputPatterns>$(MSBuildCacheIgnoredInputPatterns);$(PackagesConfigFile)</MSBuildCacheIgnoredInputPatterns>