[clang] Use the VFS to get the OpenMP entry info (#160935)

This PR uses the VFS to get the OpenMP entry info instead of going
straight to the real file system. This matches the behavior of other
input files of the compiler.

Author: jansvoboda11

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -1542,10 +1542,8 @@ static llvm::TargetRegionEntryInfo getEntryInfoFromPresumedLoc(
     SourceManager &SM = CGM.getContext().getSourceManager();
     PresumedLoc PLoc = SM.getPresumedLoc(BeginLoc);
 
-    llvm::sys::fs::UniqueID ID;
-    if (llvm::sys::fs::getUniqueID(PLoc.getFilename(), ID)) {
+    if (CGM.getFileSystem()->exists(PLoc.getFilename()))
       PLoc = SM.getPresumedLoc(BeginLoc, /*UseLineDirectives=*/false);
-    }
 
     return std::pair<std::string, uint64_t>(PLoc.getFilename(), PLoc.getLine());
   };