[Flang] Stop building multiple verisons of the OpenMP library

Summary:
We do not need to build for all of these architectures. Since the
infrastructure uses the natively created packager binary we can rely on
the support for generic targets. This is the same thing the OpenMP /
libc projects use now.

Depends on #126655

Author: jhuber6

flang/cmake/modules/AddFlangOffloadRuntime.cmake

@@ -96,36 +96,14 @@ macro(enable_omp_offload_compilation files)
     if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" AND
         "${CMAKE_C_COMPILER_ID}" MATCHES "Clang")
 
-      set(all_amdgpu_architectures
-        "gfx700;gfx701;gfx801;gfx803;gfx900;gfx902;gfx906"
-        "gfx908;gfx90a;gfx90c;gfx940;gfx1010;gfx1030"
-        "gfx1031;gfx1032;gfx1033;gfx1034;gfx1035;gfx1036"
-        "gfx1100;gfx1101;gfx1102;gfx1103;gfx1150;gfx1151"
-        "gfx1152;gfx1153"
-        )
-      set(all_nvptx_architectures
-        "sm_35;sm_37;sm_50;sm_52;sm_53;sm_60;sm_61;sm_62"
-        "sm_70;sm_72;sm_75;sm_80;sm_86;sm_89;sm_90"
-        )
-      set(all_gpu_architectures
-        "${all_amdgpu_architectures};${all_nvptx_architectures}"
-        )
-      # TODO: support auto detection on the build system.
-      if (FLANG_OMP_DEVICE_ARCHITECTURES STREQUAL "all")
-        set(FLANG_OMP_DEVICE_ARCHITECTURES ${all_gpu_architectures})
-      endif()
-      list(REMOVE_DUPLICATES FLANG_OMP_DEVICE_ARCHITECTURES)
-
-      string(REPLACE ";" "," compile_for_architectures
-        "${FLANG_OMP_DEVICE_ARCHITECTURES}"
-        )
-
       set(OMP_COMPILE_OPTIONS
         -fopenmp
         -fvisibility=hidden
         -fopenmp-cuda-mode
-        --offload-arch=${compile_for_architectures}
-        # Force LTO for the device part.
+        -fopenmp-targets=amdgcn-amd-amdhsa,nvptx64-nvidia-cuda
+        -Xopenmp-target=amdgcn-amd-amdhsa -march=''
+        -Xopenmp-target=nvptx64-nvidia-cuda -march=''
+        -nogpulib
         -foffload-lto
         )
       set_source_files_properties(${files} PROPERTIES COMPILE_OPTIONS