[make] print build_mode to console
[make] print build_mode to console

Summary: Useful to know if your build is going to take 40s or 4 minutes.

Reviewed By: jeremydubreil

Differential Revision: D5872878

fbshipit-source-id: 1d370f3

jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer