[testsuite gfortran] partial fix for secnds*.f

[Dominique Dhumieres]

> Observance of parentheses is a requirement in the C90 and C99 standards,
> as it always was in Fortran.  According to my understanding, gcc doesn't
> break this part of the standard, even with -ffast-math.

I hope so, but some time ago I had a problem with (a+f)-f simplified
as 'a' with optimization. I'll have to dig my archives to see if this
is still true.