HIP allows __fp16 as function arguments and return value by passing
-fallow-half-arguments-and-returns to clang through hipcc.
https://reviews.llvm.org/D133885 removed -fallow-half-arguments-and-returns
and add a TargetInfo member to control it.
This caused regressions in some HIP apps (https://github.com/ROCm-Developer-Tools/HIP/issues/3178).