Reject illegal ARM iWMMXt instructions

[Richard Earnshaw]

> The ARM assembler in iWMMXt mode currently silently accepts some
> instructions which are not actually supported.  When the
> w{ld,str}{b,h,w,d} instructions are used with a control register,
> conditional execution is not permitted, and only the word size is
> permitted.  The assembler used to silently discard any condition and
> force the instruction to word size.
> 
> I have checked in this patch to make the assembler give an error in
> such cases.
> 
> Ian
> 

There should really be a test-case for this as well.  See 
testsuite/gas/arm/armv1-bad.[sl]

R.