This patch implements atomic intrinsics atomic.load.add (sub,and,or,xor,

This patch implements atomic intrinsics atomic.load.add (sub,and,or,xor,
nand), atomic.swap and atomic.cmp.swap, all in i8, i16 and i32 versions.
The intrinsics are implemented by creating pseudo-instructions, which are
then expanded in the method MipsTargetLowering::EmitInstrWithCustomInserter.

Patch by Sasa Stankovic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132323 91177308-0d34-0410-b5e6-96231b3b80d8