[libc] Search the compiler's path for GPU utility tools (llvm#82712)

Summary:
We need some extra tools for the GPU build. Normally we search for these
from the build itself, but in the case of a `LLVM_PROJECTS_BUILD` or
some other kind of external build, this directory will not be populated.
However, the GPU build already requires that the compiler is an
up-to-date clang, which should always have these present next to the
binary. Simply add this as a fallback search path. Generally we want it
to be the second, because it would pick up someone install and then
become stale.

Author: jhuber6

libc/cmake/modules/prepare_libc_gpu_build.cmake

@@ -17,9 +17,10 @@ if(NOT LLVM_LIBC_FULL_BUILD)
 endif()
 
 # Identify the program used to package multiple images into a single binary.
+get_filename_component(compiler_path ${CMAKE_CXX_COMPILER} DIRECTORY)
 find_program(LIBC_CLANG_OFFLOAD_PACKAGER
              NAMES clang-offload-packager NO_DEFAULT_PATH
-             PATHS ${LLVM_BINARY_DIR}/bin)
+             PATHS ${LLVM_BINARY_DIR}/bin ${compiler_path})
 if(NOT LIBC_CLANG_OFFLOAD_PACKAGER)
   message(FATAL_ERROR "Cannot find the 'clang-offload-packager' for the GPU "
                       "build")
@@ -45,7 +46,7 @@ elseif(LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
   # Using 'check_cxx_compiler_flag' does not work currently due to the link job.
   find_program(LIBC_NVPTX_ARCH
                NAMES nvptx-arch NO_DEFAULT_PATH
-               PATHS ${LLVM_BINARY_DIR}/bin)
+               PATHS ${LLVM_BINARY_DIR}/bin ${compiler_path})
   if(LIBC_NVPTX_ARCH)
     execute_process(COMMAND ${LIBC_NVPTX_ARCH}
                     OUTPUT_VARIABLE arch_tool_output