AArch64: update Clang for merged arm64/aarch64 triples.

The main subtlety here is that the Darwin tools still need to be given "-arch
arm64" rather than "-arch aarch64". Fortunately this already goes via a custom
function to handle weird edge-cases in other architectures, and it tested.

I removed a few arm64_be tests because that really isn't an interesting thing
to worry about. No-one using big-endian is also referring to the target as
arm64 (at least as far as toolchains go). Mostly they date from when arm64 was
a separate target and we *did* need a parallel name simply to test it at all.
Now aarch64_be is sufficient.

llvm-svn: 213744
diff --git a/clang/lib/Driver/ToolChains.h b/clang/lib/Driver/ToolChains.h
index 8e5cf04..6f5b256 100644
--- a/clang/lib/Driver/ToolChains.h
+++ b/clang/lib/Driver/ToolChains.h
@@ -362,7 +362,7 @@
 
   bool isKernelStatic() const override {
     return !isTargetIPhoneOS() || isIPhoneOSVersionLT(6, 0) ||
-           getTriple().getArch() == llvm::Triple::arm64;
+           getTriple().getArch() == llvm::Triple::aarch64;
   }
 
 protected: