Implement builtins for Neon half-precision float conversions.
Also tweak the VCVT_F32_F16 entry in arm_neon.td to be more consistent with
the other floating-point conversion builtins.  Radar 8068427.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@121916 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed