[PATCH] Warn on use of vector initializers in ARM BE mode

[Tim Northover]

Hi James,

> Tim, you're right. However Alp I think has the solution - if we only fire when a NEON vector type is used, it restricts to only types that are defined in arm_neon.h.

It's certainly a big step in the right direction, but I don't think it
solves the issue completely. #including arm_neon.h is an obvious way
to get the vector types even if you have no intention of using the
intrinsics (it's even mentioned in the AAPCS). The NEON vector types
are also the only way to get ABI conformance in Clang (i.e. correct
name mangling), so you might well use them even without arm_neon.h.

I can still see the argument for having the warning (though I'm not
entirely sure I'm convinced by it), but at the very least I think
those issues mean it should be controllable (-Wno-whatever).

Cheers.

Tim.