make: Export the CC variable to sub shells.

The CC environment variable is used by the bin_to_o.sh script to build an
object module which has a binary file as the data in one of its sections. To
ensure it's set even if the parent environment didn't set it, export it from
make into sub shells.

Change-Id: I588160949537ad8f2bebf78cca32979e74336d64
1 file changed