[clang] Invert condition refactored in llvm#160935 (llvm#161583)

The PR llvm#160935 incorrectly replaced `llvm::sys::fs::getUniqueID()` with
`llvm::vfs::FileSystem::exists()` in a condition. That's incorrect,
since the first function returns `std::error_code` that evaluates to
`true` when there is an error (file doesn't exist), while the new code
does the opposite. This PR fixes that issue by inverting the
conditional.

Co-authored-by: ronlieb <ron.lieberman@amd.com>

Author: jansvoboda11

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -1566,7 +1566,7 @@ static llvm::TargetRegionEntryInfo getEntryInfoFromPresumedLoc(
     SourceManager &SM = CGM.getContext().getSourceManager();
     PresumedLoc PLoc = SM.getPresumedLoc(BeginLoc);
 
-    if (CGM.getFileSystem()->exists(PLoc.getFilename()))
+    if (!CGM.getFileSystem()->exists(PLoc.getFilename()))
       PLoc = SM.getPresumedLoc(BeginLoc, /*UseLineDirectives=*/false);
 
     return std::pair<std::string, uint64_t>(PLoc.getFilename(), PLoc.getLine());