kbuild: Set cflags before including arch Makefile

Please note that this patch, even if UML-related, should be immediately
discussed for merging in mainline, if possible. The UML patch to handle
this has therefore been separated.

Patch purpose:
If arch/$(ARCH)/Makefile is included before adding -O2 (and the rest) to
CFLAGS, I must duplicate the addition of it to USER_CFLAGS for UML.
So let's fix this.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -456,15 +456,6 @@ else
 include/linux/autoconf.h: ;
 endif
 
-include $(srctree)/arch/$(ARCH)/Makefile
-
-# Default kernel image to build when no specific target is given.
-# KBUILD_IMAGE may be overruled on the commandline or
-# set in the environment
-# Also any assingments in arch/$(ARCH)/Makefiel take precedence over
-# this default value
-export KBUILD_IMAGE ?= vmlinux
-
 # The all: target is the default when no target is given on the
 # command line.
 # This allow a user to issue only 'make' to build a kernel including modules
@@ -488,6 +479,15 @@ endif
 # warn about C99 declaration after statement
 CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 
+include $(srctree)/arch/$(ARCH)/Makefile
+
+# Default kernel image to build when no specific target is given.
+# KBUILD_IMAGE may be overruled on the commandline or
+# set in the environment
+# Also any assingments in arch/$(ARCH)/Makefiel take precedence over
+# this default value
+export KBUILD_IMAGE ?= vmlinux
+
 #
 # INSTALL_PATH specifies where to place the updated kernel and system map
 # images.  Uncomment if you want to place them anywhere other than root.