build: cleanup jimtcl generated configure.gnu

We use configure.gnu to pass options to the jimtcl submodule.
Make sure a distclean removes any generated files

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

Makefile.am

@@ -86,6 +86,7 @@ uninstall-hook:
 
 distclean-local:
 	rm -rf Doxyfile doxygen
+	rm -f $(srcdir)/jimtcl/configure.gnu
 	
 DISTCLEANFILES = doxygen.log