[clang] [-Wunsafe-buffer-usage] Allow strerror for %s in printf-like calls (PR #175208)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt requested changes to this pull request.

In principle this is fine, though I think that this should be written such that all the standard "returns a null terminated string" APIs can be tested - do we have an existing optimized "does this string match any of this statically known set of strings?" tool? 

https://github.com/llvm/llvm-project/pull/175208