doc: change example to existing Makefile fragment

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Documentation/kbuild/makefiles.txt

@@ -921,8 +921,9 @@ When kbuild executes, the following steps are followed (roughly):
 	Often, the KBUILD_CFLAGS variable depends on the configuration.
 
 	Example:
-		#arch/x86/Makefile
-		cflags-$(CONFIG_M386) += -march=i386
+		#arch/x86/boot/compressed/Makefile
+		cflags-$(CONFIG_X86_32) := -march=i386
+		cflags-$(CONFIG_X86_64) := -mcmodel=small
 		KBUILD_CFLAGS += $(cflags-y)
 
 	Many arch Makefiles dynamically run the target C compiler to