[SimplifyLibCalls] Fix memchr expansion for constant strings.

The C standard says "The memchr function locates the first
occurrence of c (converted to an unsigned char)[...]".  The expansion
was missing the conversion to unsigned char.

Fixes https://bugs.llvm.org/show_bug.cgi?id=39041 .

Differential Revision: https://reviews.llvm.org/D55947



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350775 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed