Revert "[libc++][NFC] atomic::wait use public API on macOS" (#148705)

Reverts llvm/llvm-project#147146

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
```