* config.gcc (m68k-*-aout*, m68k-*-coff*, m68020-*-elf*, m68k-*-elf*)
(m68010-*-netbsdelf*, m68k*-*-netbsdelf*, m68k*-*-openbsd*)
(m68k-*-uclinuxoldabi, m68k-*-uclinux*, m68k-*-linux*)
(m68k-*-rtems*): Use tm_file rather than m68k/m68k.h and
explicitly set MOTOROLA to 1.
* config/m68k/m68k.h (MOTOROLA): Simplify definition accordingly.