[llvm] [Flang][runtime] Fix RENAME intrinsic, remove trailing blanks (PR #159123)

[via llvm-commits]

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@@ -65,8 +65,20 @@ void RTDEF(Rename)(const Descriptor &path1, const Descriptor &path2,
   char *pathDst{EnsureNullTerminated(
       path2.OffsetElement(), path2.ElementBytes(), terminator)};
 
+  // Trim trailing blanks
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jeanPerier wrote:

@kparzysz, note that you can still deal with blank terminated files on UNIX system after this patch by using `rename("test_trailing  "//char(0), "new_name  "//char(0))`.

This is consistent not only with gfortran, but also with IFX and nvfortran/classic flang implementations. Given this is a legacy lib3f intrinsic, we must stick to the existing behaviors here. 

https://github.com/llvm/llvm-project/pull/159123