kbuild: define clean before including kbuild file

Defining clean before including the kbuild file give us knowledge when
the kbuild file is included for cleaning. This is rarey usefull - but in
a corner case in klibc this proved necessary.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
---

scripts/Makefile.clean

@@ -7,6 +7,11 @@ src := $(obj)
 .PHONY: __clean
 __clean:
 
+# Shorthand for $(Q)$(MAKE) scripts/Makefile.clean obj=dir
+# Usage:
+# $(Q)$(MAKE) $(clean)=dir
+clean := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.clean obj
+
 # The filename Kbuild has precedence over Makefile
 include $(if $(wildcard $(srctree)/$(src)/Kbuild), \
                         $(srctree)/$(src)/Kbuild, $(srctree)/$(src)/Makefile)
@@ -89,8 +94,3 @@ $(subdir-ymn):
 # If quiet is set, only print short version of command
 
 cmd = @$(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))' &&) $(cmd_$(1))
-
-# Shorthand for $(Q)$(MAKE) scripts/Makefile.clean obj=dir
-# Usage:
-# $(Q)$(MAKE) $(clean)=dir
-clean := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.clean obj