Add __warn_memset_zero_len builtin as a workaround for glibc issue

Glibc issue: https://sourceware.org/bugzilla/show_bug.cgi?id=25399
The fix consist in considering the missing function as a builtin lowered to a nop.

Differential Revision: https://reviews.llvm.org/D72869

(cherry picked from commit d2934179)