[Flang] Fix test not updated after 'clang' case change

Summary:
The shared 'clang' code changed this slightly but did not update the
flang test.

Author: jhuber6

flang/test/Driver/omp-driver-offload.f90

@@ -172,13 +172,25 @@
 
 ! Check that `-gpulibc` includes the LLVM C libraries for the GPU.
 ! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
-! RUN:      --offload-arch=gfx90a --offload-arch=sm_52 \
+! RUN:      --offload-arch=sm_52 \
 ! RUN:      -gpulibc %s 2>&1 \
-! RUN:   | FileCheck --check-prefix=LIBC-GPU %s
-! LIBC-GPU: "-lcgpu"{{.*}}"-lmgpu"
+! RUN:   | FileCheck --check-prefix=LIBC-GPU-NVPTX %s
+! LIBC-GPU-NVPTX: "-lcgpu-nvptx"{{.*}}"-lmgpu-nvptx"
 
 ! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
-! RUN:      --offload-arch=gfx90a --offload-arch=sm_52 \
+! RUN:      --offload-arch=sm_52 \
 ! RUN:      -nogpulibc %s 2>&1 \
-! RUN:   | FileCheck --check-prefix=NO-LIBC-GPU %s
-! NO-LIBC-GPU-NOT: "-lcgpu"{{.*}}"-lmgpu"
+! RUN:   | FileCheck --check-prefix=NO-LIBC-GPU-NVPTX %s
+! NO-LIBC-GPU-NVPTX-NOT: "-lcgpu-nvptx"{{.*}}"-lmgpu-nvptx"
+
+! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
+! RUN:      --offload-arch=gfx90a \
+! RUN:      -gpulibc %s 2>&1 \
+! RUN:   | FileCheck --check-prefix=LIBC-GPU-AMDGPU %s
+! LIBC-GPU-AMDGPU: "-lcgpu-amdgpu"{{.*}}"-lmgpu-amdgpu"
+
+! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
+! RUN:      --offload-arch=gfx90a \
+! RUN:      -nogpulibc %s 2>&1 \
+! RUN:   | FileCheck --check-prefix=NO-LIBC-GPU-AMDGPU %s
+! NO-LIBC-GPU-AMDGPU-NOT: "-lcgpu-amdgpu"{{.*}}"-lmgpu-amdgpu"