ARM & AArch64: merge NEON absolute compare intrinsics

There was an extremely confusing proliferation of LLVM intrinsics to implement
the vacge & vacgt instructions. This combines them all into two polymorphic
intrinsics, shared across both backends.
ARM & AArch64: combine implementation of vcaXYZ intrinsics

Now that the back-end intrinsics are more regular, there's no need for the
special handling these got in the front-end, so they can be moved to
EmitCommonNeonBuiltinExpr.
[CMake] check-dragonegg-validator: Add dependencies to llvm tools.