Makefiles: allow CC to be overridden

When using external builders such as bitbake, CC needs to be overridden as
the CROSS_COMPILE variable is not always used.  Using the ?= operator to
assign CC does this.
glives.c: remove extraneous include

Previous versions of code made use of libconfig, and this was cut out in
the public release and substituted with command line parameters.  This
removed the dependency on libconfig and reduced code complexity.  Remove
leftover #include line.