[llvm] [LIT] Add support for `%basename_s` to get base name of source file (PR #110993)

[Alexander Richardson via llvm-commits]

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@@ -535,6 +535,7 @@ TestRunner.py:
  %{fs-tmp-root}          root component of file system paths pointing to the test's temporary directory
  %{fs-sep}               file system path separator
  %t                      temporary file name unique to the test
+ %basename_s             The last path component of %s
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arichardson wrote:

I see this is consistent with the already existing basename_t, but I feel that it would make a lot more sense if this was consistent with `%{s:real}` and `%{/s:regex_replacement}` as below, i.e. `%{s:basename}`.

https://github.com/llvm/llvm-project/pull/110993