x86, 64-bit: add prototype for x86_64_start_kernel()

Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/asm-x86/setup.h

@@ -56,6 +56,8 @@ extern void probe_roms(void);
 extern unsigned long init_pg_tables_start;
 extern unsigned long init_pg_tables_end;
 
+#else
+void __init x86_64_start_kernel(char *real_mode);
 #endif /* __i386__ */
 #endif /* _SETUP */
 #endif /* __ASSEMBLY__ */