[ARMv8] Add support for 32-bit MIN/MAXNM and directed rounding.

This patch adds support for the 32bit numeric max/min and directed round-to-integral NEON intrinsics that were added as part of v8, along with unit tests.

Patch by Graham Hunter!



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217242 91177308-0d34-0410-b5e6-96231b3b80d8