x86: Fix ASM_X86__ header guards

Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:

a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/irq.h

@@ -1,5 +1,5 @@
-#ifndef ASM_X86__IRQ_H
-#define ASM_X86__IRQ_H
+#ifndef _ASM_X86_IRQ_H
+#define _ASM_X86_IRQ_H
 /*
  *	(C) 1992, 1993 Linus Torvalds, (C) 1997 Ingo Molnar
  *
@@ -47,4 +47,4 @@ extern void native_init_IRQ(void);
 /* Interrupt vector management */
 extern DECLARE_BITMAP(used_vectors, NR_VECTORS);
 
-#endif /* ASM_X86__IRQ_H */
+#endif /* _ASM_X86_IRQ_H */