When processing inline asm that contains errors, make sure we can recover gracefully by creating an UNDEF SDValue for the inline asm statement before returning from SelectionDAGBuilder::visitInlineAsm. This is necessary for consumers that don't exit on the first error that is emitted (e.g. clang) and that would assert later on.
Fixes PR24071.
Can you wrap up most of these calls into a helper like SelectionDAGBuilder::emitInlineAsmError(const Twine &) so that we don't forget to call setValue in the future?