See https://bugs.gentoo.org/show_bug.cgi?id=235789
2008-09-09 Martin von Gagern

--- xorg-server-1.5.0.orig/hw/kdrive/vesa/vm86.h	2008-09-09 17:24:59.000000000 +0200
+++ xorg-server-1.5.0/hw/kdrive/vesa/vm86.h	2008-09-09 18:01:53.000000000 +0200
@@ -67,6 +67,13 @@
 #include "os.h"
 #endif
 
+#ifndef IF_MASK
+#define IF_MASK X86_EFLAGS_IF
+#endif
+#ifndef IOPL_MASK
+#define IOPL_MASK X86_EFLAGS_IOPL
+#endif
+
 typedef unsigned char	U8;
 typedef unsigned short	U16;
 typedef unsigned int	U32;