crti.asm: add pic support.

        * config/score/crti.asm: add pic support.
        * config/score/crtn.asm: add pic support.
        * config/score/score.h: remove builtin_define("__pic__").
        * config/score/score.c: add TARGET_RTX_COST macro.
        * config/score/score.md: PIC support for call/sibcall pattern.
        * config/score/mul-div.S: add pic support.
        * config/score/t-score-elf: update MULTILIB_OPTIONS.
        * ChangeLog: add shengguo as another score maintainer.
        * config.sub: add score support in it.

From-SVN: r117771