[PATCH][PR libgfortran/78314] Fix ieee_support_halting

[FX]

> disabling/enabling makes this api a lot heavier
> than before, but trapping cannot be decided at
> compile-time, although the result may be cached,
> i think this should not be a frequent operation.
> 
> otoh rereading my patch i think i fail to restore
> the original exception state correctly.

Well, if we have no choice, then let’s do it. (With an updated patch)

FX