optim.opts: add -ffast-math -fno-finite-math-only

-ffast-math works fine provided that std::isnan() and std::isfinite()
work which is taken care of by -fno-finite-math-only

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@7304 2fb0f335-1f38-0410-981e-8018bf24f1b0

optim.opts

@@ -14,6 +14,8 @@ GXX_WARNING_OPTS=" \
 GXX_OPTS=" \
     -fno-strict-aliasing \
     -fstrict-overflow \
+    -ffast-math \
+    -fno-finite-math-only \
     -O3 \
     -march=native \
     -DNDEBUG=1"