coreboot's Makefile exports a lot of variables that influence make sub- processes (e.g. for Kconfig). We don't want these variables leak into sub-processes for (lib)payload builds, hence unexport them. Change-Id: I7d65c0aa6d4550bd6600c437e838339af69496da Signed-off-by: Nico Huber <nico.h@gmx.de> Reviewed-on: https://review.coreboot.org/c/coreboot/+/48939 Reviewed-by: Angel Pons <th3fanbus@gmail.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>