config.gcc (a29k*-*-rtems*, [...]): New targets.

        * config.gcc (a29k*-*-rtems*, arm*-*-rtems*, c4x-*-rtems*,
        h8300-*-rtems*, hppa1.1-*-rtems, *mips*-*-rtems*): New targets.
        * config.gcc (*-rtems*): Add support for gthr-rtems.h.
        * gthr-rtems.h, config/a29k/rtems.h, config/arm/rtems-elf.h,
        config/h8300/rtems.h, config/mips/rtems.h: New files.

From-SVN: r38094