* libc/machine/m68k/m68kasm.h: New file.
* libc/machine/m68k/setjmp.S: Remove common definitions and
place in m68kasm.h. Include "m68kasm.h".
* libc/machine/m68k/memcpy.S: Include "m68kasm.h" and use
SYM() macro when referencing function name.
* libc/machine/m68k/memset.S: Ditto.