macOS clang base missing __GCC_DESTRUCTIVE_SIZE and __GCC_CONSTRUCTIVE_SIZE #319

Summary

Clang 19 and later predefine __GCC_DESTRUCTIVE_SIZE and
__GCC_CONSTRUCTIVE_SIZE. libc++ uses them unconditionally from C++17 on, in
<__new/interference_size.h>, to define
std::hardware_destructive_interference_size and
std::hardware_constructive_interference_size.

The native macOS bases for clang mode
(bases/cmake-native/macos-arm/clang/lib/predefined_macros.txt, the x86_64
one, and their byte-identical copies in the target-configuration directories
lib_macos_arm64/ and lib_macos_x86_64/) do not define them. The Linux docker bases do (for example
bases/docker/dev-env/clang/lib_linux_riscv64/predefined_macros.txt).

The macOS file appears to be a snapshot of Apple clang 15: it sets
__apple_build_version__ 15000309. That stays so even when the front end
emulates a newer clang with --clang_version, as HACKING.md says to do
with the scraped version. The current Command Line Tools ship Apple clang 21
and its libc++, so every C++17 or later translation unit that reaches <new>
fails.

Reproducer

#ifndef __GCC_DESTRUCTIVE_SIZE
#error "__GCC_DESTRUCTIVE_SIZE is not defined"
#endif
#ifndef __GCC_CONSTRUCTIVE_SIZE
#error "__GCC_CONSTRUCTIVE_SIZE is not defined"
#endif
int x = __GCC_DESTRUCTIVE_SIZE + __GCC_CONSTRUCTIVE_SIZE;

cpfe --clang_version=210000 --c++20 --no_wrap_diagnostics interference.cpp