devel/llvm15: Pull in a patch fixing a crash in libclang.

This unbreaks KDevelop with C++ projects.
Relevant discussion on the KDE Bugzilla: https://bugs.kde.org/show_bug.cgi?id=438249#c33

Approved by: brooks
Differential Revision: https://reviews.freebsd.org/D42089

(cherry picked from commit 5d388efd8d1cc1369bfbdc4b247b26abd001e366)