[Bug libfortran/78314] [aarch64] ieee_support_halting does not report unsupported fpu traps correctly

[nsz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78314

--- Comment #12 from nsz at gcc dot gnu.org ---
this got reverted because of bug 88678

and because compile time and runtime support_halting are different.

the compile time value is unconditionally true, which is wrong for
aarch64 and arm:

gcc/fortran/simplify.c:
gfc_expr *
simplify_ieee_support (gfc_expr *expr)
{
  /* We consider that if the IEEE modules are loaded, we have full support
     for flags, halting and rounding, which are the three functions
     (IEEE_SUPPORT_{FLAG,HALTING,ROUNDING}) allowed in constant
     expressions. One day, we will need libgfortran to detect support and
     communicate it back to us, allowing for partial support.  */

  return gfc_get_logical_expr (gfc_default_logical_kind, &expr->where,
                               true);
}

i don't know how to change this to false for IEEE_SUPPORT_HALTING
on aarch64 and arm targets, but that would be a possible fix.