[PATCH, Fortan] fix initialization of flag_errno_math and flag_associative_math

[VandeVondele Joost]

Dominque, 

after Janne's OK, and FX judgement, I wonder if you have reached a conclusion. If so, the fsf assignment is now complete, and the patch could be applied.

Joost

> Ok for trunk. Thanks!

Please don't rush! The behavior of -fno-signed-zeros -fno-trapping-math
implying associative math has been changed (as in reverted) between r165758
(implied associative math) and r165930 (lost associative math). AFAICT
it could be due to 165823. Investigating! I am also lookinf for the introduction
of *frontend_set*.

TIA

Dominique