alien_interface_fortran should be disable if fortran not found

[guignont]

Here is a log
...
-- [ ALIEN ] Not found : mpifort
...
...
-- [ ALIEN ] ** Load executable component alien_interface_fortran.exe
CMake Error at cmake/build-system/commands/user/logFatalError.cmake:3 (message):
FATAL ERROR : undefined library mpifort linked with
alien_interface_fortran.exe
Call Stack (most recent call first):
cmake/build-system/commands/user/commit.cmake:83 (logFatalError)
cmake/build-system/commands/user/commit.cmake:160 (__commit_executable)
test/AlienInterfaceC/Fortran/CMakeLists.txt:30 (commit)