Makefile: compiler target: separate fixed text and value by a colon

Continue to use the "key: value" format like for the C compiler.
Use only shell code for TARGET_OS comparison.

Change-Id: I69959c20aa2e43ed67b3057c37e964a34cdab136
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/58617
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72252
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed