Corth - GAS syntax support

Assembly can now be generated for the GNU assembler (as) using the -GAS CCLI flag.

To assemble and link GAS assembly, Corth uses gcc by default. gcc links to the C RunTime uneless otherwise told, so this means if you are having linking issues GAS will likely be a wonderful alternative, or if you just prefer to use gcc to compile things.

This is a large step forward in compatibility; Mac seems to be the only logical next step.