scripts/Makefile.lib: speed up build process

This piece of bash code starts running randomly and slows
down building process by 40-50% and when hitting techpack driver
building slows down to Pentium 4 speeds.

Change-Id: Idebeabaee2a57e77560d531a356e6c3e1981436c
Signed-off-by: Yaroslav Furman <yaro330@gmail.com>
Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>