Fix for ROOT-8510 - CMake: default config on MacOS fails due to fortran

cmake/modules/CheckCompiler.cmake

@@ -9,6 +9,9 @@ if(fortran)
     set(CMAKE_Fortran_COMPILER CMAKE_Fortran_COMPILER-NOTFOUND)
   endif()
   enable_language(Fortran OPTIONAL)
+  if(NOT CMAKE_Fortran_COMPILER)
+    set(CMAKE_Fortran_COMPILER_LOADED)   # FindBLAS/LAPACK tests CMAKE_Fortran_COMPILER_LOADED
+  endif()
 else()
   set(CMAKE_Fortran_COMPILER CMAKE_Fortran_COMPILER-NOTFOUND)
 endif()