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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175686 91177308-0d34-0410-b5e6-96231b3b80d8
