[SimplifyLibCalls] Transform printf("%s", str) --> puts(str)/noop

Before this change LLVM cannot simplify printf in following cases:

printf("%s", "") --> noop
printf("%s", str"\n") --> puts(str)

From the other hand GCC can perform such transformations for many years:
https://godbolt.org/z/7nnqbedfe

Differential Revision: https://reviews.llvm.org/D100724