Improve the build system

This allows Frida to use capstone's build system as-is:
https://github.com/frida/frida-build-env/commit/d618aaca4c4b7365c4a5b225ff58551c005eca80

I also made the output much less verbose by default (all other Frida-modules get this for free, and it's something I can recommend as it makes it much easier to spot warnings and anomalies in the build output). So when you need to debug compiler flags it's just a matter of adding `V=1`, e.g. `make V=1`.