Pass MATHX_LIB by reference
Pass MATHX_LIB by reference

The previous code is considered a syntax error by recent rustc builds.

bgarrels/rust-lua53,SpaceManiac/rust-lua53,jcmoyer/rust-lua53,jcmoyer/rust-lua53,jcmoyer/rust-lua53,SpaceManiac/rust-lua53,bgarrels/rust-lua53,SpaceManiac/rust-lua53,mneumann/rust-lua53,jcmoyer/rust-lua53,SpaceManiac/rust-lua53,mneumann/rust-lua53