How do you work with subdirectory in GNUstep GNUmakefiles?

[Lloyd Dupont]

(NOTE: I have this problem with MinGW on Windows)

My code span 2 directories:
"./"
"./ImportExport"

Now I could declare all my file in GNUmakefile's variable: 
"MyTool-ObjC_OBJC_FILES"

But when it comes to compile file in the subdirectory: "./ImportExport"
I get an error:
+-----------------------------------------+
ImportExport/MyObject.m:86: fatal error: opening dependency file 
shared_obj/ImportExport/MyObject.d: No such file or directory

+-----------------------------------------+

I could fix it manually by creating the directory: 
"./shared_obj/ImportExport/"
Or by creating a target: "requiredDirs" and calling "make requiredDirs", but 
it would be nice to have the (default) target "all" create it.
How do I do that?