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>
diff --git a/arch/x86/include/asm/prctl.h b/arch/x86/include/asm/prctl.h
index e7ae34e..fe68114 100644
--- a/arch/x86/include/asm/prctl.h
+++ b/arch/x86/include/asm/prctl.h
@@ -1,5 +1,5 @@
-#ifndef ASM_X86__PRCTL_H
-#define ASM_X86__PRCTL_H
+#ifndef _ASM_X86_PRCTL_H
+#define _ASM_X86_PRCTL_H
 
 #define ARCH_SET_GS 0x1001
 #define ARCH_SET_FS 0x1002
@@ -7,4 +7,4 @@
 #define ARCH_GET_GS 0x1004
 
 
-#endif /* ASM_X86__PRCTL_H */
+#endif /* _ASM_X86_PRCTL_H */