Create a MachineBasicBlock for created IR-level BasicBlock

While running the lit tests for the most recent version of D45916
(https://reviews.llvm.org/D45916), I found that a couple tests for this pass
suddenly started segfaulting. Since the outliner wasn't actually doing anything
to the code in either of these tests I got curious.

I found that the pass doesn’t completely create the machine-level constructs
necessary to actually add a MachineFunction and MachineBasicBlock to the
module. This patch adds in those missing bits. After this, adding the
outliner before this pass won’t cause it to segfault.

You can recreate this behaviour by adding the MachineOutliner directly before
the pass and having it return false immediately.

https://reviews.llvm.org/D46330

llvm-svn: 331307