Fix incremental build when dummy version.cpp is generated (dotnet/cor…

…eclr#8547)

This change fixes a problem with incremental build on Unix. When the
version.cpp is generated by the build.sh as a dummy one with no real
version stamp in it, it is recreated every time the build.sh is run.
That means that build needs to rebuild that file and also re-link
all the components that include it.
This change tests the file presence and contents before actually
regenerating it.

Commit migrated from dotnet/coreclr@101168c

src/coreclr/build.sh

@@ -167,16 +167,22 @@ build_coreclr()
  if [ $__SkipConfigure == 0 ]; then
  # if msbuild is not supported, then set __SkipGenerateVersion to 1
  if [ $__isMSBuildOnNETCoreSupported == 0 ]; then __SkipGenerateVersion=1; fi
- # Drop version.c file
+ # Drop version.cpp file
  __versionSourceFile=$__IntermediatesDir/version.cpp
  if [ $__SkipGenerateVersion == 0 ]; then
  "$__ProjectRoot/run.sh" build -Project=$__ProjectDir/build.proj -generateHeaderUnix -NativeVersionSourceFile=$__versionSourceFile $__RunArgs $__UnprocessedBuildArgs
  else
+ # Generate the dummy version.cpp, but only if it didn't exist to make sure we don't trigger unnecessary rebuild
  __versionSourceLine="static char sccsid[] __attribute__((used)) = \"@(#)No version information produced\";"
- echo $__versionSourceLine > $__versionSourceFile
+ if [ -e $__versionSourceFile ]; then
+ read existingVersionSourceLine < $__versionSourceFile
+ fi
+ if [ "$__versionSourceLine" != "$existingVersionSourceLine" ]; then
+ echo $__versionSourceLine > $__versionSourceFile
+ fi
  fi
 
- pushd "$__IntermediatesDir"
+ pushd "$__IntermediatesDir"
  # Regenerate the CMake solution
  __ExtraCmakeArgs="-DCLR_CMAKE_TARGET_OS=$__BuildOS -DCLR_CMAKE_PACKAGES_DIR=$__PackagesDir -DCLR_CMAKE_PGO_INSTRUMENT=$__PgoInstrument"
  echo "Invoking \"$__ProjectRoot/src/pal/tools/gen-buildsys-clang.sh\" \"$__ProjectRoot\" $__ClangMajorVersion $__ClangMinorVersion $__BuildArch $__BuildType $__CodeCoverage $__IncludeTests $generator $__ExtraCmakeArgs $__cmakeargs"