[PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Nick Clifton]

Hi Julian,

> ChangeLog (gas):
> 
>     * config/tc-arm.c (md_assemble): Improve diagnostic when attempting
>     to use ARM instructions on non-ARM-supporting cores.
>     (autoselect_thumb_from_cpu_variant): New function. Switch on Thumb
>     mode automatically based on cpu variant.
>     (md_begin): Call above function.
> 
> ChangeLog (gas/testsuite):
> 
>     * gas/arm/noarm.s: Add test for disabled ARM insns.
>     * gas/arm/noarm.d: Drive test for above.
>     * gas/arm/noarm.l: Expected error output.
> 

Approved - please apply.

Cheers
   Nick