linux.h (CC1_SPEC): Define it only if not defined.

linux.h (CC1_SPEC): Define it only if not defined.

        * config/linux.h (CC1_SPEC): Define it only if not defined.

        * config/m68k/linux.h (CC1_SPEC): Undefine it before include
        <linux.h>

        * config/linux.h (DEFAULT_VTABLE_THUNKS): New. Defined as 1 if
        USE_GNULIBC_1 is not defined.

        * config/alpha/linux.h (DEFAULT_VTABLE_THUNKS): New. Defined
        as 1.
        * config/rs6000/linux.h (DEFAULT_VTABLE_THUNKS): Ditto.

        * config/sparc/linux.h (DEFAULT_VTABLE_THUNKS): New. Defined
        as 1 if USE_GNULIBC_1 is not defined.
Linux patches from HJ.

From-SVN: r14960