swr/rast: fix intrinsic/function for LLVM 7 compatibility

Converted from x86 VFMADDPS intrinsic to generic LLVM intrinsic, and
removed createInstructionSimplifierPass, which were both removed in LLVM
7.0.0

These changes combine patches we received from the community and our own
internal patches

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>
Tested-by: Chuck Atkins <chuck.atkins@kitware.com>
(cherry picked from commit 8c872ac2)