ELF symbol table field st_other support,
excluding visibility bits.

Mips specific standalone assembler directive "set at".

This directive changes the general purpose register
that the assembler will use when given the symbolic
register name $at.

This does not include negative testing. That will come
in a future patch.

A side affect of this patch recognizes the different
GPR register names for temporaries between old abi
and new abi so a test case for that is included.

Contributer: Vladimir Medic