[PATCH] Add silent Makefile rules

[Eli Zaretskii]

> From: Simon Marchi <simon.marchi@ericsson.com>
> CC: Simon Marchi <simon.marchi@polymtl.ca>
> Date: Fri, 2 Mar 2018 15:25:16 -0500
> 
> The gnulib/libiberty builds are still verbose, but we have no control
> over that (until we contribute a silent mode to those projects too).

??? Isn't gnulib/Makefile.in our file?  If so, we can add there
anything we want, including the macros you defined in
gdb/Makefile.in.  Right?