Properly support more asm constraints
Fixes tests:
	CodeGen/Generic/2007-04-27-InlineAsm-X-Dest.ll
	CodeGen/Generic/2007-04-27-LargeMemObject.ll
	CodeGen/Generic/2007-12-17-InvokeAsm.ll
	CodeGen/Generic/2008-02-20-MatchingMem.ll
	CodeGen/Generic/asm-large-immediate.ll
	CodeGen/Generic/inline-asm-mem-clobber.ll
	Transforms/BranchFolding/2007-10-19-InlineAsmDirectives.ll