all settable params for m68k toolchain now start with `M68K_` (#7)

[tehKaiN]

fixes #7

• replaced MCRT with M68K_CRT
• added M68K_TOOLCHAIN_PATH arg which generates TOOLCHAIN_PATH variable

I see that TOOLCHAIN_PATH var is also set in other toolchains, and I think it's a good because project cmakelists can only check single variable if they need it and not each of the flavors, but it kinda breaks the convention of making all the params starting with the same prefix. I'm not very happy with my addition of M68K_TOOLCHAIN_PATH but I think it makes it more discoverable. Let me know what you think about it before you merge this.

Perhaps it'd be better to scrap common prefix and just list the values of all optional parameters using message(STATUS ...) at the beginning, or is that too much clutter for console?

[MBeijer]

the M68K_TOOLCHAIN_PATH part was in the cmake toolchain because you had used it elsewhere. TOOLCHAIN_PATH is used in the modules.

I think M68K prefix is fine for the specifics for the 68k gcc, since I don't know if you set cpu/fpu stuff all that often on PPC.

Because Ideally, the point with these CMake files, is that one build script goes a long way for building the same app for multiple targets. If every toolchain had it's own prefix, that point would be invalid. :)