[SimplifyLibCalls] Mark known arguments with nonnull
Reviewers: efriedma, jdoerfert
Reviewed By: jdoerfert
Subscribers: ychen, rsmith, joerg, aaron.ballman, lebedev.ri, uenoku, jdoerfert, hfinkel, javed.absar, spatel, dmgreen, llvm-commits
Differential Revision: https://reviews.llvm.org/D53342
llvm-svn: 372091