[llvm] [FileCheck] Handle CHECK-EMPTY at EOF without trailing newline (PR #196576)

[Joel E. Denny via llvm-commits]

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jdenny-ornl wrote:

Please extend the test suite with two more cases that have the same issue:
- Successful `CHECK-EMPTY`.
- `CHECK`, which seems like a good representative for directives that require patterns and thus must fail in this case.  Please put this one in a separate test file.

https://github.com/llvm/llvm-project/pull/196576