[RISCV] Enable MachineOutliner by default under -Oz for RISCV

[RISCV] Enable MachineOutliner by default under -Oz for RISCV

Enable default outlining when the function has the minsize attribute.

`addr-label.ll` crashed after enabling this, so a barrier is added before
instruction selection as a workaround.

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D122213