LLVM runtime shared libraries.

This port provides only the shared libraries (libLLVM.so, libLTO.so,
libRemarks.so) needed at runtime by consumers like mesa-dri that use
LLVM for JIT compilation (llvmpipe) and GPU shader compilation (AMDGPU).

This is a much smaller package than the full devel/llvm15 port, which
also includes the compiler toolchain, headers, static libraries, and
development tools.