[clang] [clang-tools-extra] [clang][AST] Fix StmtProfile handling of GCCAsmStmt asm strings and clobbers (PR #201481)

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IamYJLee wrote:

> > I'm not much familiar with clang AST Visitor testing, but is there any unit or other tests for `clang/lib/AST`? If so, we better make test there as well. Apart from this, lgtm with nit
> 
> It is fine generally if we have lit test. But I didn't notice the lit test doesn't belong to clang itself. Yeah, it is better to have a lit test under clang. We wrote unit tests less than lit test.

@vbvictor @ChuanqiXu9 
Thanks for the review.
I couldn't find any existing tests for `StmtProfile` and `VisitGCCAsmStmt`, so I'm not sure where the new test should be added. Could you suggest the appropriate place for it?

https://github.com/llvm/llvm-project/pull/201481