Add conditional option for MKL_FFTW.

CMakeLists.txt

@@ -305,10 +305,8 @@ if (MORSE_DISTRIB_DIR OR EXISTS "${CMAKE_SOURCE_DIR}/CMakeModules/morse/")
   #
   # FFT option
   #
+ CMAKE_DEPENDENT_OPTION(SCALFMM_USE_MKL_AS_FFTW "Set to ON to use MKL FFTW" ON  "SCALFMM_USE_FFT;SCALFMM_USE_MKL_AS_BLAS" OFF )
   if( SCALFMM_USE_FFT )
-
-    option( SCALFMM_USE_MKL_AS_FFTW "Set to ON to use MKL FFTW" OFF )
-
     message(STATUS "SCALFMM USE FFT Configure:")
 
     if( SCALFMM_USE_MKL_AS_FFTW )