buildroot

lua: use target LDFLAGS

This adds '-static' to the link command when BR2_STATIC_LIBS=y, making the lua
binary really static.

Cc: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit 7e48c824309641c9eec41ee3dd7292a579888965)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>