Bug 313560 – [CMake] Set --std=c++17 for the libatomic probe

• Status: RESOLVED
• Resolution: FIXED
• Component: CMake

[zak ridouh]

The atomic source test uses std::atomic<std::optional<double>>, which
requires C++17. check_cxx_source_compiles inherits the compiler's
default C++ standard, and on compilers that default to C++14 or
earlier the probe fails with "no member named 'optional' in namespace
'std'". Pre-312202@main this was silent and the build proceeded
(builtins suffice on arm64 without libatomic). 312202@main promoted
the failure to FATAL_ERROR, which broke the CMake build on those
compilers.

Set CMAKE_REQUIRED_FLAGS to --std=c++2b around the probe, mirroring
the existing pattern at the std::filesystem detection a few lines
below. unset() restores the previous state.

[Radar WebKit Bug Importer]

<rdar://problem/175777090>

[zak ridouh]

Pull request: https://github.com/WebKit/WebKit/pull/63816

[EWS]

Committed 312222@main (cfb69a99823a): <https://commits.webkit.org/312222@main>

Reviewed commits have been landed. Closing PR #63816 and removing active labels.

[Adrian Perez]

Reopening for a follow-up.

[Adrian Perez]

Pull request: https://github.com/WebKit/WebKit/pull/63832

[EWS]

Committed 312266@main (07ed81f30130): <https://commits.webkit.org/312266@main>

Reviewed commits have been landed. Closing PR #63832 and removing active labels.

[EWS]

Committed 305877.462@webkitglib/2.52 (b7eabfc1efa4): <https://commits.webkit.org/305877.462@webkitglib/2.52>

Reviewed commits have been landed. Closing PR #63872 and removing active labels.