[llvm] [InferAttrs] Mark errnomem-setting libcalls as such (PR #124742)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> We also have to worry about accesses of implementation details in headers. If any library calls are implemented as inline functions in headers, they may access memory that is logically inaccessible.

This is in part an already existing issue, isn't it? Agree that, during LTO, chances of hitting this would be higher with the patch though.

> I'm not very confident there are no non-libcall ways to access all of these even within the defined API.

This is what I was kind of worried about too initially, that such APIs may access some (memory) state that could be still program-visible. Might not be the case for locale, but definitely is for unsetenv, as you noted. Restricted libc functions back to errnomem only; this can be relieved further if needed.

https://github.com/llvm/llvm-project/pull/124742