[llvm] r238311 - We always have an InstPrinter.

[Rafael Espíndola]

> Could we take the parameter by reference instead of pointer?

That gets into the wonderful world of TargetRegistry.h.

The MCAsmStreamer takes ownership of this, so the natural way would be
to pass a std::unique_ptr. But TargetRegistry.h would have to call
std::move, and to do that it would have to know the size of the
instprinter instead of just having a forward declaration.

But TargetRegistry.h is in Support, so it cannot include a header from MC.

Getting ownership of something passed by reference would be even more
confusing IMHO.

Cheers,
Rafael