[clang] [clang][analyzer] Support 'fflush' in the StdLibraryFunctionsChecker (PR #76557)

[Ben Shi via cfe-commits]

benshi001 wrote:

> Looks good to me, my only nitpick is that perhaps you could use more descriptive test names instead of using `_0` and `_1` suffixes.
> 
> Also, perhaps wait a bit (until next year ;) ) before merging this to give other reviewers a chance to look at it.

Thanks for your suggestion. I have renamed the test functions to more meaningful names.

https://github.com/llvm/llvm-project/pull/76557