Add actual fix and release note

Author: DeinAlptraum

clang/docs/ReleaseNotes.rst

@@ -557,6 +557,8 @@ clang-format
 
 libclang
 --------
+- Fixed a bug in ``clang_File_isEqual`` that sometimes led to different 
+  in-memory files to be considered as equal.
 - Added ``clang_visitCXXMethods``, which allows visiting the methods
   of a class.
 

clang/tools/libclang/CIndex.cpp

@@ -5170,7 +5170,7 @@ int clang_File_isEqual(CXFile file1, CXFile file2) {
 
   FileEntryRef FEnt1 = *cxfile::getFileEntryRef(file1);
   FileEntryRef FEnt2 = *cxfile::getFileEntryRef(file2);
-  return FEnt1.getUniqueID() == FEnt2.getUniqueID();
+  return FEnt1 == FEnt2;
 }
 
 CXString clang_File_tryGetRealPathName(CXFile SFile) {