Makefile: fix up CROSS_COMPILE and READABLE_ASM interaction.
When the READABLE_ASM cc-option tests were added they were done so prior
to the arch Makefile include, resulting in cc-option being run on the
host cc instead of the factoring in the cross prefix set up by the
architecture.
This bumps the include back up so that cc-option actually runs on the
compiler that we're building with.