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

[arrowd]

Summary

This unbreaks KDevelop with C++ projects.

Relevant discussion on the KDE Bugzilla: https://bugs.kde.org/show_bug.cgi?id=438249#c33

[brooks]

I'd typically name the patch something like patch-backport-48fb6659610a3 to make it clear that I won't need it in newer versions, but this is fine (especially since llvm15 isn't going to be the basis for the next release (llvm18)).