I've committed this to the OG12 branch to remove some test failures. We 
probably ought to have something on mainline also, but a proper fix 
would be better.

Without this. the libgomp.oacc-c-c++-common/private-variables.c testcase 
fails to compile due to an ICE.  The OpenACC worker broadcasting code is 
creating SLP optimizable loads and stores in amdgcn address-space-4. 
Previously this was "ok" as SLP didn't work with less that 64-lane 
vectors, but the newly implemented smaller vectors are working as 
intended and optimizing this.

Unfortunately the vectorizer is losing the address-space data from the 
intermediate types, and it all falls apart during expand when it tries 
the convert a 32-bit address into a 64-bit address and that's not 
something that works. At first sight it looks like we could possibly 
make that work with POINTERS_EXTEND_UNSIGNED, but that only changes the 
error message. Fundamentally we need to make sure that various instances 
of "vectype" have the correct address space, but my attempts to do so 
showed that that's a larger task than I have time for right now.

This patch simply prevents the vectorizer working in the case where it 
would break. This should not be a regression because this code didn't 
vectorize at all, previously.

Andrew