[libc] Use -nolibc -nostdlib++ -nostartfiles for hermetic test link.

[sivachandra]

Summary

We previously used a more stricter -nostdlib option which was also removing
compiler-rt/libgcc.

[jhuber6]

Does this also need to be applied to this?

foreach(lib LibcHermeticTest LibcHermeticTestMain)    
  target_include_directories(${lib} PRIVATE ${LIBC_BUILD_DIR}/include)    
  target_compile_options(${lib}    
      PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} -ffreestanding -nostdlib -nostdlib++)    
endforeach()

[sivachandra]

In D149683#4313423, @jhuber6 wrote:

Does this also need to be applied to this?

foreach(lib LibcHermeticTest LibcHermeticTestMain)    
  target_include_directories(${lib} PRIVATE ${LIBC_BUILD_DIR}/include)    
  target_compile_options(${lib}    
      PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} -ffreestanding -nostdlib -nostdlib++)    
endforeach()

Creating static/object libraries does not involve the linker so may be not required?

[jhuber6]

In D149683#4313428, @sivachandra wrote:

In D149683#4313423, @jhuber6 wrote:

Does this also need to be applied to this?

foreach(lib LibcHermeticTest LibcHermeticTestMain)    
  target_include_directories(${lib} PRIVATE ${LIBC_BUILD_DIR}/include)    
  target_compile_options(${lib}    
      PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} -ffreestanding -nostdlib -nostdlib++)    
endforeach()

Creating static/object libraries does not involve the linker so may be not required?

I'm assuming this solution won't work on the GPU anyway since we don't have a compiler-rt there anyway. But for the CPU it should be fine as long as the final link has it.

[sivachandra]

Add -nostdlib++ also.

[mikhail.ramalho]

-nostdlib++ is a clang-only flag, gcc fails with:

g++-12: error: unrecognized command-line option ‘-nostdlib++’; did you mean ‘-nostdlib’?

libc/cmake/modules/LLVMLibCTestRules.cmake

target_include_directories(
     PRIVATE
       ${LIBC_SOURCE_DIR}
       ${LIBC_BUILD_DIR}
       ${LIBC_BUILD_DIR}/include
   )
   target_compile_options(${fq_build_target_name}
       PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} ${HERMETIC_TEST_COMPILE_OPTIONS})
 
-  target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
+  target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib++ -static)
   target_link_libraries(
     ${fq_build_target_name}
     PRIVATE
       ${HERMETIC_TEST_LINK_LIBRARIES}
       libc.startup.${LIBC_TARGET_OS}.crt1
       LibcHermeticTestMain LibcHermeticTest
       # The NVIDIA 'nvlink' linker does not currently support static libraries.
       $<$<NOT:$<BOOL:${LIBC_GPU_TARGET_ARCHITECTURE_IS_NVPTX}>>:${fq_target_name}.__libc__>)