makefiles: rename target "all" to "byte", and move it after "opt"

The "all" target is a bit of a misnomer, as it doesn't build everything; it builds byte-code. Rename it to "byte".

Additionally, nowadays compilation to native instructions should be available on most platforms, so put "opt" first, making it the default target.

Signed-off-by: Laszlo Ersek lersek@redhat.com