CheckFortranFunctionExists

macro which checks if the Fortran function exists

CHECK_FORTRAN_FUNCTION_EXISTS(FUNCTION VARIABLE)

FUNCTION - the name of the Fortran function
VARIABLE - variable to store the result
           Will be created as an internal cache variable.

The following variables may be set before calling this macro to modify the way the check is run:

CMAKE_REQUIRED_LIBRARIES = list of libraries to link