Mips direct object xgot support

This patch provides support for the MIPS relocations:

    *)  R_MIPS_GOT_HI16
    *)  R_MIPS_GOT_LO16
    *)  R_MIPS_CALL_HI16
    *)  R_MIPS_CALL_LO16

These are used for large GOT instruction sequences.

Contributer: Jack Carter
llvm-svn: 168471