Building llvm 9 fails on macOS 10.15

[mrArkwright]

Building llvm 9 with brew install --build-from-source llvm-hs/llvm/llvm-9 fails on macOS 10.15 on my machine.

The macports community already found a fix for this: https://trac.macports.org/ticket/61477. The ticket concerns macOS 11.0 but as far as I understand this also applies to 10.15 if MacOSX11.0.sdk is present (macports/macports-ports@eabdb0e). The error I'm getting is the exact same as in that ticket:

:info:build [ 27%] Building C object lib/Support/CMakeFiles/LLVMSupport.dir/regexec.c.o
:info:build cd /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/build/lib/Support && /usr/bin/clang -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/build/lib/Support -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/lib/Support -I/opt/local/include/libxml2 -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/build/include -I/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/include -pipe -Os -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk -fPIC -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wcovered-switch-default -Wdelete-non-virtual-dtor -Wstring-conversion -DNDEBUG -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk -mmacosx-version-min=11.0 -o CMakeFiles/LLVMSupport.dir/regexec.c.o -c /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/lib/Support/regexec.c
:info:build /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc:169:31: error: invalid application of 'sizeof' to an incomplete type 'struct stat64'
:info:build   unsigned struct_stat64_sz = sizeof(struct stat64);
:info:build                               ^     ~~~~~~~~~~~~~~~
:info:build /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc:169:45: note: forward declaration of '__sanitizer::stat64'
:info:build   unsigned struct_stat64_sz = sizeof(struct stat64);
:info:build                                             ^
:info:build /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc:195:33: error: invalid application of 'sizeof' to an incomplete type 'struct statfs64'
:info:build   unsigned struct_statfs64_sz = sizeof(struct statfs64);
:info:build                                 ^     ~~~~~~~~~~~~~~~~~
:info:build /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-9.0/clang-9.0/work/llvm-9.0.1.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc:195:47: note: forward declaration of '__sanitizer::statfs64'
:info:build   unsigned struct_statfs64_sz = sizeof(struct statfs64);
:info:build                                               ^
:info:build 2 errors generated.
:info:build make[2]: *** [projects/compiler-rt/lib/sanitizer_common/CMakeFiles/RTSanitizerCommonNoHooks.osx.dir/sanitizer_platform_limits_posix.cc.o] Error 1

Setting -DDARWIN_osx_ARCHS="x86_64;x86_64h" seems to resolve the issue. However when -DLLVM_BUILD_EXTERNAL_COMPILER_RT is used that setting doesn't seem to be taken into account. Finally to make the build work without -DLLVM_BUILD_EXTERNAL_COMPILER_RT again I also had to specify -DCMAKE_OSX_ARCHITECTURES="x86_64".

Is removing -DLLVM_BUILD_EXTERNAL_COMPILER_RT a problem? To be honest I'm not sure why it was turned on and what the implications of turning it off are. For my compiler project with llvm-hs the build works fine.

[tmcdonell]

I'm still on 10.14 but I'll see if I can find a 10.15 box to try it on.

The -DLLVM_BUILD_EXTERNAL_COMPILER_RT flag was required to fix some other problem a long time ago, but maybe it's not necessary anymore (maybe when building for aarch64?) so perhaps we can remove it.