Fixes PR 17106 (explicitly typed enums are formatted differently).

Before:
 enum X : int { A, B, C };

After:
 enum X : int {
   A,
   B,
   C
 };
[ARMv8] Implement the new DMB/DSB operands.

This removes the custom ISD Node: MEMBARRIER and replaces it
with an intrinsic.