Revert "remove -frecursive from default FFLAGS"

This reverts commit 42a7ffa87cda15497e0b6c46bd76b2b4df44f365.

Jae-hyeon wrote:

-frecursive was there for thread-safety. Without the flag, there is a
potential danger that different threads might share a local array in a
fortran function.  Please see the manual of gfortran.