Turn on -function-sections
Turn on -function-sections

This helps the linker coalesce multiple copies of the runtime (with the
flag --gc-sections). Turns out this wasn't properly happening before.


Former-commit-id: 0c8c09fa7eaced11eef91989256b7b80595fd35a
darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide