quota: fix static linking

The aim of this patch is to fix bug #7574, i.e fix the static linking
of the quota package. It does so by introducing a patch to the quota
build system that generalizes the use of $(LIBS), and then changes
quota.mk to use LIBS instead of LDFLAGS to link against intl and tirpc
when needed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>