Fix a 4x slowdown in llc -asm-verbose caused by the use of

WriteAsOperand in more places.

Now that more things are using WriteAsOperand, its behavior of
constructing a TypePrinting object and populating it with strings for all
the numbered types in the Module on each call is a significant bottleneck.
Fancier solutions could be pursued here, but for now, just bypass the
TypePrinting overhead in obvious cases.

llvm-svn: 78906