* config.gcc: Add crx-elf support.

        * doc/contrib.texi: Mention crx.
        * doc/extend.texi: Document crx extensions.
        * doc/install.texi: Document crx install.
        * doc/invoke.texi: Document crx options.
        * doc/md.texi: Document crx constraints.

        * config/crx/crx-protos.h: New file.
        * config/crx/crx.c: New file.
        * config/crx/crx.h: New file.
        * config/crx/crx.md: New file.
        * config/crx/crx.opt: New file.
        * config/crx/t-crx: New file.

From-SVN: r102278