Makefile: Revise build options for Linux specific headers

Clean up the feature target by outsourcing the test to an own variable.
Change the print output and don't write to the build-details file.

This is in preparation for further changes.

Change-Id: I18fc27252afb49fa7d1f2787faee2b5b669275aa
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/58627
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72254
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
5 files changed