cmake: add /usr/lib/llvm13 to searched paths

Alpine linux installs llvm to this path and currently patches zig's
cmake file in order to build zig from source.

https://git.alpinelinux.org/aports/tree/testing/zig/llvm-include.patch?id=0c3f7850bef38fb4c63fc6af5c14724e5311b0cc
49a7ceb5bcIsaac Freund committed on 5/5/2022, 6:51:48 AM· committed by Andrew Kelleyparentba12705
1 file changedLine totals unavailable