[patch, libgfortran] PR32611 Print sign of negative zero

[Brooks Moses]

Jerry DeLisle wrote:
> The attached patch provides a solution to this PR.
> 
> The patch uses the signbit function to determine if a zero value is negative. 
> If so, the sign is emitted.  If -std=legacy is specified at compile time, the 
> negative sign for zero values is not emitted.
> 
> This patch requires -std=legacy to be used to pass NIST.  This is because F77 
> explicitly prohibits printing the negative sign for zero values.
[...]
> OK for trunk?

This needs documenting, of course.

If you aren't sure of the best place to document it, feel free to create 
a documentation PR about it and assign it to me, and I'll get to it 
sometime in August when I have time to think again.  :)

In particular, note that this changes the meaning of the -std= option.
Currently, it only affects what language features are accepted, 
rejected, or warned about, but any program that compiles will have the 
same behavior regardless of which -std= option was used to compile it.
Your patch changes this, which is IMHO a fairly significant little change.

- Brooks