tests/Makefile.inc: Cleanup, change assignments to immediate

Change assignments from lazy to immediate to make them more
deterministic.
Remove unused `CUSTOM_MUSIC=n` argument from vboot build recipe.

BUG=none
TEST=sudo USE=abi_x86_32 emerge dev-util/cmocka && \
     make clean-unit-tests && make unit-tests
BRANCH=none

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: Ic746dadd5c90fb00c9c4cc974e7f212713b49224
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/depthcharge/+/3100145
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Commit-Queue: Yu-Ping Wu <yupingso@chromium.org>
1 file changed