Summary:
During MIPS implementation work for FreeBSD, John Baldwin (jhb@FreeBSD.org)
found that gcc 6.x emits calls to __ffssi2() when compiling libc and some
userland programs in the base system.
Add it to compiler-rt's builtins, based off of the existing __ffsdi2()
implementation. Also update the CMake files and add a test case.
Reviewers: howard.hinnant, weimingz, rengolin, compnerd
Reviewed By: weimingz
Subscribers: dberris, mgorny, llvm-commits, emaste
Differential Revision: https://reviews.llvm.org/D31721
llvm-svn: 299675