Makefile: Use immediate assignement when calculating SYSTEM

This makes null builds run with just "make" go from 4.6 seconds
to 73ms, since it only calls config.guess once.
[NaCl] Add sanity checks to nacl-regal.sh

Update NaCl build in accordance with recent Makefile changes.
NaCl binaryes all live in the same folder and have architecutre
in thier filename.

Automatically create nmf file.

Add LOG_CC to Makefile.