AArch64/ARM64: remove AArch64 from tree prior to renaming ARM64.

I'm doing this in two phases for a better "git blame" record. This
commit removes the previous AArch64 backend and redirects all
functionality to ARM64. It also deduplicates test-lines and removes
orphaned AArch64 tests.

The next step will be "git mv ARM64 AArch64" and rewire most of the
tests.

Hopefully LLVM is still functional, though it would be even better if
no-one ever had to care because the rename happens straight
afterwards.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209576 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64/ARM64: move ARM64 into AArch64's place

This commit starts with a "git mv ARM64 AArch64" and continues out
from there, renaming the C++ classes, intrinsics, and other
target-local objects for consistency.

"ARM64" test directories are also moved, and tests that began their
life in ARM64 use an arm64 triple, those from AArch64 use an aarch64
triple. Both should be equivalent though.

This finishes the AArch64 merge, and everyone should feel free to
continue committing as normal now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209577 91177308-0d34-0410-b5e6-96231b3b80d8
CodeGen: Make MachineBasicBlock::back skip to the beginning of the last bundle.

This makes front/back symmetric with begin/end, avoiding some confusion.
Added instr_front/instr_back for the old behavior, corresponding to
instr_begin/instr_end. Audited all three in-tree users of back(), all
of them look like they don't want to look inside bundles.

Fixes an assertion (PR19815) when generating debug info on mips, where a
delay slot was bundled at the end of a branch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209580 91177308-0d34-0410-b5e6-96231b3b80d8
MachineVerifier: Clean up some syntactic weirdness left behind by find&replace.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209581 91177308-0d34-0410-b5e6-96231b3b80d8