[Libcalls, Attrs] Annotate libcalls with noundef

I think we can use here same logic as for nonnull.

strlen(X) - X must be noundef => valid pointer.

for libcalls with size arg, we add noundef only if size is known and greater than 0 - so pointers must be noundef (valid ones)

Reviewed By: jdoerfert, aqjune

Differential Revision: https://reviews.llvm.org/D95122