[AArch64] Fix verifier error when outlining indirect calls

The MachineOutliner for AArch64 transforms indirect calls into indirect
tail calls, replacing the call with the TCRETURNri pseudo-instruction.
This pseudo lowers to a BR, but has the isCall and isReturn flags set.

The problem is that TCRETURNri takes a tcGPR64 as the register argument,
to prevent indiret tail-calls from using caller-saved registers. The
indirect calls transformed by the outliner could use caller-saved
registers. This is fine, because the outliner ensures that the register
is available at all call sites. However, this causes a verifier failure
when the register is not in tcGPR64. The fix is to add a new
pseudo-instruction like TCRETURNri, but which accepts any GPR.

Differential revision: https://reviews.llvm.org/D52829

llvm-svn: 343959