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>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 5500ab55d042..5787d55a20b6 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -150,7 +150,7 @@ CPPFLAGS_vmlinux.lds	:= -Upowerpc
 
 BOOT_TARGETS = zImage zImage.initrd znetboot znetboot.initrd vmlinux.sm uImage
 
-.PHONY: $(BOOT_TARGETS)
+PHONY += $(BOOT_TARGETS)
 
 boot := arch/$(ARCH)/boot