add a new EmitInlineAsm function to asmprinter to handle inline asm.

add a new EmitInlineAsm function to asmprinter to handle inline asm.
If we have an MCAsmStreamer, we continue to emit asm textually,
otherwise we (currently) emit an error to errs and ignore it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100289 91177308-0d34-0410-b5e6-96231b3b80d8