Clang: use -std=c23 for Clang 18+
Canonical flag changed in LLVM commit 13629b140801870feff855ca168edf6b34dbef8d.
Backport: release
Edited by Brad King
Canonical flag changed in LLVM commit 13629b140801870feff855ca168edf6b34dbef8d.
Backport: release