[libc++] Switch to the officially documented APIs for implementing ulock_{wait,wake} on Apple

[ldionne]

While discussing with @huixie90 and Apple folks about #109290, it was noticed that we were still using forward-declarations of __ulock_wait and __ulock_wake. Instead, the public API os_sync_wait_on_address is now provided and documented, so we should switch to that. This can be a simple NFC refactoring.

[Michael137]

This is failing to build on our public macOS CI: https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake-sanitized/

06:48:56  FAILED: libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o 
06:48:56  /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/bin/clang++ --target=arm64-apple-darwin23.1.0 -DLIBCXX_BUILDING_LIBCXXABI -DLIBC_NAMESPACE=__llvm_libc_common_utils -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1 -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxxabi/include -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/cmake/Modules/../../libc -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -O3 -DNDEBUG -std=c++23 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -mmacosx-version-min=14.1 -fPIC -UNDEBUG -faligned-allocation -nostdinc++ -fvisibility-inlines-hidden -fvisibility=hidden -fsized-deallocation -Wall -Wextra -Wnewline-eof -Wshadow -Wwrite-strings -Wno-unused-parameter -Wno-long-long -Werror=return-type -Wextra-semi -Wundef -Wunused-template -Wformat-nonliteral -Wzero-length-array -Wdeprecated-redundant-constexpr-static-def -Wno-nullability-completeness -Wno-user-defined-literals -Wno-covered-switch-default -Wno-suggest-override -Wno-error -fdebug-prefix-map=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/include -MD -MT libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -MF libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o.d -o libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -c /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp
06:48:56  /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp:46:12: fatal error: 'os/os_sync_wait_on_address.h' file not found
06:48:56     46 | #  include <os/os_sync_wait_on_address.h>
06:48:56        |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
06:48:56  1 error generated.

This is the configuration the failing bots are running:

06:25:12  + sw_vers
06:25:12  ProductName:		macOS
06:25:12  ProductVersion:		14.1
06:25:12  BuildVersion:		23B74
06:25:12  + xcodebuild -version
06:25:12  Xcode 15.2
06:25:12  Build version 15C5500c

The Intel bots are building fine though. Probably because they're on a newer OS where the headers are available?

10:03:35  + sw_vers
10:03:35  ProductName:		macOS
10:03:35  ProductVersion:		15.1.1
10:03:35  BuildVersion:		24B91
10:03:35  + xcodebuild -version
10:03:39  Xcode 16.2
10:03:39  Build version 16C5031c
10:03:39  + cmake --version
10:03:39  cmake version 3.30.2

[huixie90]

@ldionne what shall we do? Do we officially support the older macOS version ?

[ldionne]

Libc++'s support policy is to support the latest released Xcode, which is 16.4. Unfortunately, we forgot to update the documentation to reflect that (but we did update our CI coverage so that only Xcode 16.x would be tested). I'm updating the documentation here: #148651

Officially, this means that the GreenDragon bots should be updated to Xcode 16.x. Let's check if updating those quickly is feasible, otherwise we can temporarily keep the old code for a few days to get the CI back into the green.

[Michael137]

Reverted #148705 for now until we upgrade the bots. We wanted to do that anyway for other reasons. Will keep this thread updated

[ldionne]

So actually, we do support back to macOS 10.13 in the documentation, and it appears that os_sync_wait_on_address was introduced in macOS 14.4. So I think that we can only use the API conditionally based on the deployment target.