ARM64: initial backend import

This adds a second implementation of the AArch64 architecture to LLVM,
accessible in parallel via the "arm64" triple. The plan over the
coming weeks & months is to merge the two into a single backend,
during which time thorough code review should naturally occur.

Everything will be easier with the target in-tree though, hence this
commit.

llvm-svn: 205090
diff --git a/llvm/test/CodeGen/ARM64/fp.ll b/llvm/test/CodeGen/ARM64/fp.ll
new file mode 100644
index 0000000..08b1b67
--- /dev/null
+++ b/llvm/test/CodeGen/ARM64/fp.ll
@@ -0,0 +1,8 @@
+; RUN: llc < %s -march=arm64 | FileCheck %s
+
+define float @t1(i1 %a, float %b, float %c) nounwind {
+; CHECK: t1
+; CHECK: fcsel	s0, s0, s1, ne
+  %sel = select i1 %a, float %b, float %c
+  ret float %sel
+}