build: start comments at beginning of line

As the comments are indented in Makefile, they are actually echoed
on the screen. This patch makes sure that the comments actually start
at the beginning of the line, and so not echoed and ignored.

PR-URL: https://github.com/nodejs/node/pull/9375



Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>