Fix pragma-comment.c test failing on false match (#145455)

Sometimes the forbidden text `foo` or `bar` could appear in the Clang
version string metadata. Treating the version string as a `CHECK-LABEL:`
prevents this.

Fixes #145453

Author: dbartol

clang/test/CodeGen/pragma-comment.c

@@ -32,3 +32,6 @@
 // ELF: ![[space]] = !{!"with space"}
 // ELF-NOT: bar
 // ELF-NOT: foo
+// This following match prevents the clang version metadata from matching the forbidden 'foo' and 'bar' tokens.
+// This can happen if the clang version string contains a Git repo URL that includes one of those substrings.
+// ELF-LABEL: !"clang version