Add lowering of STRICT_FSETCC and STRICT_FSETCCS

These become STRICT_FCMP and STRICT_FCMPE, which then get selected to the
corresponding FCMP and FCMPE instructions, though the handling from there on
isn't fully correct as we don't model reads and writes to FPCR and FPSR.

Differential Revision: https://reviews.llvm.org/D73368