build_macros.mk: include assert and define loop macros

Loop macros make it easier for developers to include new variables to
assert or define and also help code code readability on makefiles.

Change-Id: I0d21d6e67b3eca8976c4d856ac8ccc02c8bb5ffa
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
7 files changed