Add warn_unused_result to functions that return bool in memory.h

[agnosticlines]

Building off of #310

Recent fixes (bd3914e, 173a069) addressed unchecked return values from memory_map_fixed and memory_purge. Adding __attribute__((warn_unused_result)) to the functions that return bool in memory.h would catch this class at compile time with -Werror.

Candidates: memory_map_fixed, memory_map_fixed_mte, memory_unmap, memory_protect_ro, memory_protect_rw, memory_protect_rw_metadata, memory_remap, memory_remap_fixed, memory_purge.

You could also add it to memory_set_name but every single call site ignores its return value so probably not worth it.

[thestinger]

There's no reason to add it to memory_set_name. The only case it's relevant to memory_purge is if zeroing the memory is desirable even though it failed to be freed. In practice, memory_purge won't fail. It will only fails in an extreme scenario where basic system calls aren't working. Adding the extra code paths to handle it was for nearly entirely theoretical situations and doesn't actually matter in practice. VMA exhaustion can actually happen in practice mainly due to the fact that there's an artificial limit that's often quite low so mmap, munmap and mprotect can fail with ENOMEM in cases where that happens. madvise with MADV_DONTNEED isn't going to fail with ENOMEM in practice, but it made sense to add handling for it to make sure memory still got zeroed if that did happen.

[agnosticlines]

I've just been following the fixes today and saw you fix it in one location so figured it was worth mentioning the other cases, entirely up to you what you do :-)

And yeah I figured memory_set_name didn't matter.