add support for multiple return values in inline asm. This is a step

towards PR2094.  It now compiles the attached .ll file to:

_sad16_sse2:
	movslq	%ecx, %rax
	## InlineAsm Start
	%ecx %rdx %rax %rax %r8d %rdx %rsi
	## InlineAsm End
	## InlineAsm Start
	set %eax
	## InlineAsm End
	ret

which is pretty decent for a 3 output, 4 input asm.

llvm-svn: 50386