[llvm] [FileCheck]: Fix diagnostic for trailing CHECK-NOT (PR #78412)

[Thomas Preud'homme via llvm-commits]

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@@ -0,0 +1,12 @@
+; RUN: rm %t && \
+; RUN: echo "LEADING: placeholder1" >>%t && echo "TRAILING-NOT: placeholder2" >>%t && \
+; RUN: %ProtectFileCheckOutput not FileCheck --strict-whitespace --check-prefixes LEADING,TRAILING --input-file %t %t 2>&1 | \ 
+; RUN: FileCheck %s
+; END
+
+CHECK:           error: TRAILING-NOT: excluded string found in input
+CHECK-NEXT:      TRAILING-NOT: placeholder2
+CHECK-NEXT: {{^}}              ^{{$}}
+CHECK-NEXT:      note: found here
+CHECK-NEXT:      TRAILING-NOT: placeholder2
+CHECK-NEXT: {{^}}              ^~~~~~~~~~~~{{$}}
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RoboTux wrote:

That does not seem to show the problem as the test pass even without your patch applied.

https://github.com/llvm/llvm-project/pull/78412