x86: sigframe.h: add guard macro

Impact: cleanup

Add missing guard macro _ASM_X86_SIGFRAME_H.
Signed-off-by: NHiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/include/asm/sigframe.h

+#ifndef _ASM_X86_SIGFRAME_H
+#define _ASM_X86_SIGFRAME_H
+
 #ifdef CONFIG_X86_32
 #define sigframe_ia32		sigframe
 #define rt_sigframe_ia32	rt_sigframe
@@ -59,3 +62,5 @@ struct rt_sigframe {
 	/* fp state follows here */
 };
 #endif /* CONFIG_X86_64 */
+
+#endif /* _ASM_X86_SIGFRAME_H */