[PATCH, arm] Stack the PIC register for Thumb if PIC is enabled

[Adam Nemet]

Nick,

> Sadly there is one unexpected failure with -mpic-register=6 that is
> not present without it:
> 
>         gcc.c-torture/compile/20000804-1.c -O0
> 
> I have not investigated this yet, nor have I checked to see if it
> happens without the patch applied...

If you meant -mpic-register=6 together with -mthumb then yes that
fails even without the patch.  I checked my regression-baseline logs
and also tried manually with an unpatched cc1.  I think the patch is
safe. 

I will submit a separate (unrelated) patch to fix the above failure. 

Adam