Libc++'s policy is to support only the latest released Xcode, which is
Xcode 16.x. We did update our CI jobs to Xcode 16.x, but we forgot to
update the documentation, which still mentioned Xcode 15. This patch
updates the documentation and cleans up outdated mentions of
apple-clang-15 in the test suite.
This simplifies the tests a little bit:
Fixed -> TODO(LLVM20): remove [[maybe_unused]] and `{}` scope since all
supported compilers support "Placeholder variables with no name"
*IMPORTANT: Requires Apple Clang with [P2169R4: A nice placeholder with
no name](https://wg21.link/P2169R4)*
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Co-authored-by: Hristo Hristov <zingam@outlook.com>
On z/OS int128 is disabled causing one of the cases in
`saturate_cast.pass.cpp` to fail. The failure is only in 64-bit mode.
In this case `the std::numeric_limits<long long int>::max()` is within
`std::numeric_limits<unsigned long int>::min()`
and `std::numeric_limits<unsigned long int>::max()` therefore,
saturate_cast<unsigned long int>( sBigMax) == LONG_MAX and not ULONG_MAX
as original test.
In 32-bit, `saturate_cast<unsigned long int>( sBigMax) == ULONG_MAX`
like on other platforms where int128 is enabled.
This PR is required to pass this test case on z/OS and possibly on other
platforms where int128 is not supported/enabled.
---------
Co-authored-by: Sean Perry <perry@ca.ibm.com>
