[OpenMP] Add `__CUDA_ARCH__` definition when offloading with OpenMP

[jhuber6]

Summary

Currently we define the __CUDA_ARCH__ macro only in CUDA mode. This
patch allows us to use this macro in OpenMP-offloading mode when
targeting NVPTX.

[tianshilei1992]

LG

[RKSimon]

@jhuber6 I think this or one of your other openmp commits has caused the Driver/cuda-openmp-driver.cu test failure here: https://lab.llvm.org/buildbot/#/builders/214/builds/1274/steps/6/logs/stdio

[jhuber6]

In D125256#3513596, @RKSimon wrote:

@jhuber6 I think this or one of your other openmp commits has caused the Driver/cuda-openmp-driver.cu test failure here: https://lab.llvm.org/buildbot/#/builders/214/builds/1274/steps/6/logs/stdio

Is that still failing? I saw another build-bot fail on that test as well, so I pushed a quick change and it went green. When I check a more recent build there it doesn't show the test failing.

[RKSimon]

Sorry - my mistake - its a different test failure now! Nothing to do with openmp.

clang/lib/Basic/Targets/NVPTX.cpp

return llvm::StringSwitch<bool>(Feature)
       .Cases("ptx", "nvptx", true)
       .Default(false);
 }
 
 void NVPTXTargetInfo::getTargetDefines(const LangOptions &Opts,
                                        MacroBuilder &Builder) const {
   Builder.defineMacro("__PTX__");
   Builder.defineMacro("__NVPTX__");
-  if (Opts.CUDAIsDevice) {
+  if (Opts.CUDAIsDevice || Opts.OpenMPIsDevice) {
     // Set __CUDA_ARCH__ for the GPU specified.
     std::string CUDAArchCode = [this] {
       switch (GPU) {
       case CudaArch::GFX600:
       case CudaArch::GFX601:
       case CudaArch::GFX602:
       case CudaArch::GFX700:
       case CudaArch::GFX701:

clang/test/OpenMP/driver-openmp-target.c

 // REQUIRES: x86-registered-target
+// REQUIRES: nvptx-registered-target
 // REQUIRES: clang-target-64-bits
+
 // RUN: %clang %s -c -E -dM -fopenmp=libomp -fopenmp-version=45 -fopenmp-targets=x86_64-unknown-unknown -o - | FileCheck --check-prefix=CHECK-45-VERSION %s
 // CHECK-45-VERSION: #define _OPENMP 201511
+// RUN: %clang %s -c -E -dM -fopenmp=libomp -nogpulib --offload-arch=sm_70 --offload-device-only -o - | FileCheck --check-prefix=CHECK-CUDA-ARCH %s
+// CHECK-CUDA-ARCH: #define __CUDA_ARCH__ 700