[AArch64][v8.5A] Don't create BR instructions in outliner when BTI enabled

When branch target identification is enabled, we can only do indirect
tail-calls through x16 or x17. This means that the outliner can't
transform a BLR instruction at the end of an outlined region into a BR.

Differential revision: https://reviews.llvm.org/D52869

llvm-svn: 343969