[LCG] Hoist the logic for forming a new SCC from the top of the DFSStack
into a helper function. I plan to re-use it for doing incremental
DFS-based updates to the SCCs when we mutate the call graph.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206948 91177308-0d34-0410-b5e6-96231b3b80d8
[ARM64] Enable feature predicates for NEON / FP / CRYPTO.

AArch64 has feature predicates for NEON, FP and CRYPTO instructions.
This allows the compiler to generate code without using FP, NEON
or CRYPTO instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206949 91177308-0d34-0410-b5e6-96231b3b80d8