[PATCH, Fortan] fix initialization of flag_errno_math and flag_associative_math

[FX]

> Why do you want -fno-math-errno to be the default for gfortran?
> AFAICT such default is not documented and the flag works
> (checked on your test gfortran.dg/errnocheck_1.f90).

It should be the default, and it used to be. Fortran doesn’t care about math routines setting errno (its existence is specified in C & C++ standards, but not in the Fortran standard). If I understand correctly, Joost’s patch just adapts this to a new flag handling mechanism.

FX