[libc] Enable integration tests targeting NVIDIA GPUs

[jhuber6]

Summary

This patch adds the necessary build infrastructure to build and run the
integration tests on NVIDIA GPUs. The NVIDIA nvlink linker utility is
what is ultimately used to combine these files into a single executable
image. Unfortunately, their tool does not support static libraries. So
we need to link with every object directly instead. This could be solved
by impelementing a "wrapper" utility around nvlink like we used to use
for OpenMP. But for now this should be sufficient.

[sivachandra]

libc/cmake/modules/LLVMLibCTestRules.cmake

517

What will the add_library listing on line 472 do in that case?

[jhuber6]

libc/cmake/modules/LLVMLibCTestRules.cmake

517

It'll create the library, the linker just can't use it. I wasn't sure if it was worth putting an if around.

[jhuber6]

The generator expressions should only be used for NVPTX.

libc/cmake/modules/LLVMLibCTestRules.cmake

set_target_properties(${fq_target_name}.__libc__
       PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
   set_target_properties(${fq_target_name}.__libc__
       PROPERTIES ARCHIVE_OUTPUT_NAME ${fq_target_name}.libc)
 
   set(fq_build_target_name ${fq_target_name}.__build__)
   add_executable(
     ${fq_build_target_name}
     EXCLUDE_FROM_ALL
+    # The NVIDIA 'nvlink' linker does not currently support static libraries.
+    $<$<BOOL:${LIBC_TARGET_ARCHITECTURE_IS_GPU}>:${link_object_files}>
     ${INTEGRATION_TEST_SRCS}
     ${INTEGRATION_TEST_HDRS}
   )
   set_target_properties(${fq_build_target_name}
       PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
   target_include_directories(
     ${fq_build_target_name}
     PRIVATE
target_compile_options(${fq_build_target_name} PRIVATE
                            --target=${LIBC_GPU_TARGET_TRIPLE})
   elseif(LIBC_GPU_TARGET_ARCHITECTURE_IS_NVPTX)
     target_compile_options(${fq_build_target_name} PRIVATE
                            -march=${LIBC_GPU_TARGET_ARCHITECTURE}
                            --target=${LIBC_GPU_TARGET_TRIPLE})
   endif()
 
   target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
-  target_link_libraries(${fq_build_target_name} ${fq_target_name}.__libc__
-                        libc.startup.${LIBC_TARGET_OS}.crt1
-                        libc.test.IntegrationTest.test)
+  target_link_libraries(
+    ${fq_build_target_name}
+    # The NVIDIA 'nvlink' linker does not currently support static libraries.
+    $<$<NOT:$<BOOL:${LIBC_TARGET_ARCHITECTURE_IS_GPU}>>:${fq_target_name}.__libc__>
   add_dependencies(${fq_build_target_name}
                    libc.test.IntegrationTest.test
                    ${INTEGRATION_TEST_DEPENDS})
 
   # Tests on the GPU require an external loader utility to launch the kernel.
   if(TARGET libc.utils.gpu.loader)
     get_target_property(gpu_loader_exe libc.utils.gpu.loader "EXECUTABLE")
   endif()

libc/utils/gpu/loader/CMakeLists.txt

 if(TARGET amdhsa_loader AND LIBC_GPU_TARGET_ARCHITECTURE_IS_AMDGPU)
   add_custom_target(libc.utils.gpu.loader)
   add_dependencies(libc.utils.gpu.loader amdhsa_loader)
   set_target_properties(
     libc.utils.gpu.loader
     PROPERTIES
       EXECUTABLE "$<TARGET_FILE:amdhsa_loader>"
   )
+elseif(TARGET nvptx_loader AND LIBC_GPU_TARGET_ARCHITECTURE_IS_NVPTX)
+  add_custom_target(libc.utils.gpu.loader)
+  add_dependencies(libc.utils.gpu.loader nvptx_loader)
+  set_target_properties(
+    libc.utils.gpu.loader
+    PROPERTIES
+      EXECUTABLE "$<TARGET_FILE:nvptx_loader>"
+  )
 endif()