On OS X, failing to install pkg-config results in a broken build with no obvious error

[adam-mapbox]

@ljbade

On OS X, if pkg-config is not installed before building a mason project, e.g. mapbox-gl-native for android, then the build will semi-silently fail to do the pkg-config step but proceed on to a broken build (as evidenced by errors such as not finding the headers for mason packages).

https://gist.github.com/adam-mapbox/d7202588aec6ad7c4b0b

[springmeyer]

Also https://github.com/mapbox/mapbox-gl-native/issues/609. It looks like something is messed up with return codes inside mason. I took a quick look today and came up short.