support/scripts/mkmakefile: make wrapper silent by default

support/scripts/mkmakefile: make wrapper silent by default

Suppose we use Makefile wrapper and build some project out of
buildroot tree (O=...). A command like "make
busybox-all-external-deps" will output the string "uname 022 && make
..." to stdout before the usefull information. It pollutes stdout. At
the same time if we use the same command in the buildroot source-tree
then we don't get the additional output. This patch makes wrapper
silent by default. People who prefer to see more verbose output can
use V=1.

Signed-off-by: Serj Kalichev <serj.kalichev@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>