[HIP] Fix regression about __fp16 args and return value

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
(ROCm/hip#3178).

Reviewed by: Artem Belevich

Differential Revision: https://reviews.llvm.org/D145345

Fixes: ROCm/hip#3178

Author: yxsamliu

clang/lib/Basic/Targets/AMDGPU.cpp

@@ -245,6 +245,7 @@ AMDGPUTargetInfo::AMDGPUTargetInfo(const llvm::Triple &Triple,
   MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   CUMode = !(GPUFeatures & llvm::AMDGPU::FEATURE_WGP);
   ReadOnlyFeatures.insert("image-insts");
+  HalfArgsAndReturns = true;
 }
 
 void AMDGPUTargetInfo::adjust(DiagnosticsEngine &Diags, LangOptions &Opts) {

clang/test/SemaCUDA/fp16-arg-return.cu

@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -emit-llvm -o - -triple amdgcn-amd-amdhsa -fcuda-is-device -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+__fp16 testFP16AsArgAndReturn(__fp16 x) {
+  return x;
+}