msvc + ninja + modules: Fix build when consuming fmtlib while using a Ninja generator (#4495)

Co-authored-by: Leander Schulten <Leander.Schulten@tetys.de>

CMakeLists.txt

@@ -27,12 +27,8 @@ endfunction()
 # DEPRECATED! Should be merged into add_module_library.
 function(enable_module target)
   if (MSVC)
-    if(CMAKE_GENERATOR STREQUAL "Ninja")
-      # Ninja dyndep expects the .ifc output to be located in a specific relative path
-      file(RELATIVE_PATH BMI_DIR "${CMAKE_BINARY_DIR}" "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/${target}.dir")
-    else()
+    if(NOT CMAKE_GENERATOR STREQUAL "Ninja")
       set(BMI_DIR "${CMAKE_CURRENT_BINARY_DIR}")
-    endif()
       file(TO_NATIVE_PATH "${BMI_DIR}/${target}.ifc" BMI)
       target_compile_options(${target}
         PRIVATE /interface /ifcOutput ${BMI}
@@ -40,6 +36,7 @@ function(enable_module target)
       set_target_properties(${target} PROPERTIES ADDITIONAL_CLEAN_FILES ${BMI})
       set_source_files_properties(${BMI} PROPERTIES GENERATED ON)
     endif()
+  endif ()
 endfunction()
 
 set(FMT_USE_CMAKE_MODULES FALSE)