devel/llvm15: Update to 15.0.3

See the release annoucement for included changes:
https://discourse.llvm.org/t/llvm-15-0-3-released

This is expected to be the last point release of LLVM 15.

(cherry picked from commit c908e85a90319599a90ab2b3b87a0a2a31ca9c7c)