Enable test coverage checking for buxton

Ripping off some autoconf testing from systemd here, prefer to have
something that uses autotool macros instead of the if blocks but
wasn't sure the best way to do many statements in the if block so
leaving it as is for now.

The best way to see pretty html graphs and highlighted code will be
to run configure with --enable-coverage --enable-debug then make check
followed by make coverage. Then open up coverage/test/index.html from
the source root and poke around.

Signed-off-by: William Douglas <william.douglas@intel.com>
core: memmove's 3rd argument should be a size_t

Signed-off-by: William Douglas <william.douglas@intel.com>