[PATCH V2] GAS fix alignment for aarch64-pe

[Nick Clifton]

Hi Zac,

> For the aarch64-pe target various values of '.align' causes writing of COFF files to fail.
> 
> This version of the patch differs from the first by using the write.c implementation of SUB_SEGMENT_ALIGN. This means there was no need to modify md_section_align or 
> aarch64_handle_align. The change is specific to the aarch64-pe target.
> 
> In my testing generated aligned code was correctly padded with nop.

Patch approved - please apply.

Cheers
   Nick