Follow up to r289732: Update comments in source files to reference .cpp files

Patch by Hansang Bae

llvm-svn: 289739
diff --git a/openmp/runtime/src/kmp_ftn_cdecl.cpp b/openmp/runtime/src/kmp_ftn_cdecl.cpp
index 5844bee..a3c3779 100644
--- a/openmp/runtime/src/kmp_ftn_cdecl.cpp
+++ b/openmp/runtime/src/kmp_ftn_cdecl.cpp
@@ -1,5 +1,5 @@
 /*
- * kmp_ftn_cdecl.c -- Fortran __cdecl linkage support for OpenMP.
+ * kmp_ftn_cdecl.cpp -- Fortran __cdecl linkage support for OpenMP.
  */