x11-wm/hyprland: unbreak build on 15.0-PRERELEASE

clang with debug assertions enabled (on -CURRENT) crashes when it
tries to compile a consumer code of devel/glaze. As a workaround clang
from ports has been used on -CURRENT to avoid the error. Recent switch
of the branch name from CURRENT to PRERELEASE broke the build again.

As a new workaround we use port's llvm when base clang is built with
debug assertions enabled regardless of the branch name.

PR: 289205
Reported by: Ralph Zitz <ralph@zitz.dk>
Tested by: Ralph Zitz <ralph@zitz.dk>