CMake: Don't hardcode installation folder in RPATH
CMake: Don't hardcode installation folder in RPATH

This is a bit more fragile than I'd like - setting LIBDIR to a full path
will not work as expected - but I'm not sure if there's a good way to
resolve this otherwise, and this seems to work fine by default.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer