kbuild: change kbuild to not rely on incorrect GNU make behavior

The kbuild system takes advantage of an incorrect behavior in GNU make.
Once this behavior is fixed, all files in the kernel rebuild every time,
even if nothing has changed.  This patch ensures kbuild works with both
the incorrect and correct behaviors of GNU make.

For more details on the incorrect behavior, see:

http://lists.gnu.org/archive/html/bug-make/2006-03/msg00003.html

Changes in this patch:
  - Keep all targets that are to be marked .PHONY in a variable, PHONY.
  - Add .PHONY: $(PHONY) to mark them properly.
  - Remove any $(PHONY) files from the $? list when determining whether
    targets are up-to-date or not.

Signed-off-by: Paul Smith <psmith@gnu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/kconfig/Makefile

@@ -2,7 +2,7 @@
 # Kernel configuration targets
 # These targets are used from top-level makefile
 
-.PHONY: oldconfig xconfig gconfig menuconfig config silentoldconfig update-po-config
+PHONY += oldconfig xconfig gconfig menuconfig config silentoldconfig update-po-config
 
 xconfig: $(obj)/qconf
 	$< arch/$(ARCH)/Kconfig
@@ -42,7 +42,7 @@ update-po-config: $(obj)/kxgettext
 	$(Q)rm -f arch/um/Kconfig_arch
 	$(Q)rm -f scripts/kconfig/linux_*.pot scripts/kconfig/config.pot
 
-.PHONY: randconfig allyesconfig allnoconfig allmodconfig defconfig
+PHONY += randconfig allyesconfig allnoconfig allmodconfig defconfig
 
 randconfig: $(obj)/conf
 	$< -r arch/$(ARCH)/Kconfig

scripts/kconfig/lxdialog/Makefile

@@ -7,10 +7,10 @@ check-lxdialog  := $(srctree)/$(src)/check-lxdialog.sh
 # we really need to do so. (Do not call gcc as part of make mrproper)
 HOST_EXTRACFLAGS = $(shell $(CONFIG_SHELL) $(check-lxdialog) -ccflags)
 HOST_LOADLIBES   = $(shell $(CONFIG_SHELL) $(check-lxdialog) -ldflags $(HOSTCC))
- 
-HOST_EXTRACFLAGS += -DLOCALE 
 
-.PHONY: dochecklxdialog
+HOST_EXTRACFLAGS += -DLOCALE
+
+PHONY += dochecklxdialog
 $(obj)/dochecklxdialog:
 	$(Q)$(CONFIG_SHELL) $(check-lxdialog) -check $(HOSTCC) $(HOST_LOADLIBES)