SH gas: support `.long foo@PLT' again

[Hans-Peter Nilsson]

On 6 Feb 2002, Alexandre Oliva wrote:

> A patch I installed last week broke `.long symbol@PLT', for assuming
> that a PLT fix would always contain a non-NULL subsy, as is the case
> for all GCC-generated PLT references.  However, hand-written assembly
> code in glibc didn't follow this pattern, and exposed the bug I
> introduced.  Here's a fix.  Ok to install?

Yes, but please also add a gas test-case.  I suggest following
the pattern of dsp.[sd].

brgds, H-P