make: Add comment about BUILD vs HOST
make: Add comment about BUILD vs HOST

BRANCH=none
BUG=b:176500425
TEST=none

Signed-off-by: Craig Hesling <383db090fd8ef907a606ac8a9eccd2962bc489cf@chromium.org>
Change-Id: I43839f509228299c1e31d3c824fd43c66d4a594a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2606467
Reviewed-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec