kbuild: consistently decide when to rebuild a target

Consistently decide when to rebuild a target across all of
if_changed, if_changed_dep, if_changed_rule.
PHONY targets are now treated alike (ignored) for all targets

While add it make Kbuild.include almost readable by factoring out a few
bits to some common variables and reuse this in Makefile.build.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 3cb445c..e2ad2dc 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -191,9 +191,10 @@
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call echo-cmd,cc_o_c) $(cmd_cc_o_c);				  \
 	$(cmd_modversions)						  \
-	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' > $(@D)/.$(@F).tmp;  \
+	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
+	                                              $(dot-target).tmp;  \
 	rm -f $(depfile);						  \
-	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd
+	mv -f $(dot-target).tmp $(dot-target).cmd
 endef
 
 # Built-in and composite module parts