[CMake] Chossing compiler

[Marie-Christine Vallet]

Hi,
I have a C mixed with  Fortran   and would like to be able to choose my 
fortran compiler depending on the c compiler eg ifort if I use icc or 
f77 if I use gcc. I tried this
IF ( CMAKE_COMPILER_IS_GNUCC )
        SET(CMAKE_Fortran_COMPILER f77)
ENDIF ( CMAKE_COMPILER_IS_GNUCC )
But it does not seem do anything.
Is there an other way to do it?
Thanks,
marie