[libc++][CMake] Allow merging libc++abi.a into libc++ even on Apple platforms

[ldionne]

Summary

I can't see a good reason to disallow this, even though it isn't the
standard way we build libc++ for Apple platforms.

Making this work on Apple platforms requires using different flags for
--whole-archive and removing the -D flag when running ar to merge
archives because that flag isn't supported by the ar shipped on Apple
platforms. This shouldn't be an issue since the -D option appears to be
enabled by default in GNU ar.

[smeenai]

See also D44671.

[ldionne]

In D59513#1433843, @smeenai wrote:

See also D44671.

This patch effectively supersedes D44671.

[ldionne]

Ping!

[phosek]

LGTM, thank you!

libcxx/CMakeLists.txt

 if (CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32)
   if (LIBCXX_BUILD_32_BITS AND NOT LLVM_BUILD_32_BITS) # Don't duplicate the output from LLVM
     message(STATUS "Building 32 bits executables and libraries.")
   endif()
 elseif(LIBCXX_BUILD_32_BITS)
   message(FATAL_ERROR "LIBCXX_BUILD_32_BITS=ON is not supported on this platform.")
 endif()
 
-# Check that this option is not enabled on Apple and emit a usage warning.
+# Warn users that LIBCXX_ENABLE_STATIC_ABI_LIBRARY is an experimental option.
 if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
-  if (APPLE)
-    message(FATAL_ERROR "LIBCXX_ENABLE_STATIC_ABI_LIBRARY is not supported on OS X")
-  else()
-    message(WARNING "LIBCXX_ENABLE_STATIC_ABI_LIBRARY is an experimental option")
-  endif()
   if (LIBCXX_ENABLE_STATIC AND NOT PYTHONINTERP_FOUND)
     message(FATAL_ERROR "LIBCXX_ENABLE_STATIC_ABI_LIBRARY requires python but it was not found.")
   endif()
 endif()
 
 if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     if (APPLE)
       message(FATAL_ERROR "LIBCXX_ENABLE_ABI_LINKER_SCRIPT cannot be used on APPLE targets")

libcxx/lib/CMakeLists.txt

 
 
 if (LIBCXX_GENERATE_COVERAGE AND NOT LIBCXX_COVERAGE_LIBRARY)
   find_compiler_rt_library(profile LIBCXX_COVERAGE_LIBRARY)
 endif()
 add_library_flags_if(LIBCXX_COVERAGE_LIBRARY "${LIBCXX_COVERAGE_LIBRARY}")
 
 if (APPLE AND (LIBCXX_CXX_ABI_LIBNAME STREQUAL "libcxxabi" OR
-               LIBCXX_CXX_ABI_LIBNAME STREQUAL "default"))
+               LIBCXX_CXX_ABI_LIBNAME STREQUAL "default")
+          AND NOT DEFINED LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS)
   set(LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS ON)
 endif()
 
 if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY)
+  if (APPLE)
+    add_library_flags("-Wl,-force_load" "${LIBCXX_CXX_ABI_LIBRARY}")
+  else()
     add_library_flags("-Wl,--whole-archive" "-Wl,-Bstatic")
     add_library_flags("${LIBCXX_CXX_ABI_LIBRARY}")
     add_library_flags("-Wl,-Bdynamic" "-Wl,--no-whole-archive")
+  endif()
 elseif (LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS)
   add_library_flags("${LIBCXX_CXX_ABI_LIBRARY}")
 else ()
  add_interface_library("${LIBCXX_CXX_ABI_LIBRARY}")
 endif()
 
 if (APPLE AND LLVM_USE_SANITIZER)
   if (("${LLVM_USE_SANITIZER}" STREQUAL "Address") OR

libcxx/utils/merge_archives.py

def main():
 
     files = []
     for arc in archives:
         execute_command_verbose([ar_exe, 'x', arc],
                                 cwd=temp_directory_root, verbose=args.verbose)
         out = execute_command_verbose([ar_exe, 't', arc])
         files.extend(out.splitlines())
 
-    execute_command_verbose([ar_exe, 'rcsD', args.output] + files,
+    execute_command_verbose([ar_exe, 'rcs', args.output] + files,
                             cwd=temp_directory_root, verbose=args.verbose)
 
 
 if __name__ == '__main__':
     main()
     exit_with_cleanups(0)