[ms-inline asm] If we have a single asm operand that maps to multiple

MCOperands then iterate over all of then when computing clobbers, inputs and
outputs.

On x86 the 1-to-many mapping is a memory operand that includes a BaseReg(reg),
MemScale(imm), MemIndexReg(reg), an Expr(MCExpr or imm) and a MemSegReg(reg).
Invalid register (Op.getReg() == 0) are not considered when computing clobber.

llvm-svn: 163728