meson: use llvm-config instead of cmake to fix linking errors with meson 1.2.1
What does this MR do and why?
meson: use llvm-config instead of cmake to fix linking errors with meson 1.2.1
The cmake path picks a random LLVM in /usr, which happens to be 32-bit LLVM, which fails to link with 64-bit Mesa. This is a meson, cmake, or LLVM bug.