[cli] exit with user error in case of unsupported build command
[cli] exit with user error in case of unsupported build command

Summary: This makes more sense and avoids printing a pointless backtrace. Give the user some advice while we're at it.

Reviewed By: mbouaziz

Differential Revision: D8442711

fbshipit-source-id: 65a8939

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