kernel-2: Respect portage env variables

Use BUILD_CC instead of using gcc as HOSTCC.

From upstream getoo:
https://github.com/gentoo/gentoo/commit/3dd41142d73f41e2528eefa32e760fc3083001ee

BUG=chromium:1088210
TEST=sudo emerge cross-*/linux-headers work

Change-Id: Iaae9792fb0ee4ae9b3014a8165ef26414505648c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2230207
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
1 file changed