test system: Adding compilation overrides so we can compile.

 To compile now, just run `make EXTRAFLAGS=-DRUN_TESTS`. For those
who don't know, that defines RUN_TESTS for the precompiler, which
then inserts the code in main.c inside of that #ifdef statement which
then, instead of doing normal execution, will eventually run the
test suite.

Build: CONFIRMED.

Signed-off-by: Kristofer Rye <kristofer.rye@gmail.com>