xen: add header guards to generated asm generic headers

MISRA D4.10 requires to have proper header guards in place in all header
files. Add header guards for generated asm generic headers as well.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/scripts/Makefile.asm-generic

@@ -32,7 +32,14 @@ old-headers := $(wildcard $(obj)/*.h)
 unwanted    := $(filter-out $(generic-y) $(generated-y),$(old-headers))
 
 quiet_cmd_wrap = WRAP    $@
-      cmd_wrap = echo "\#include <asm-generic/$*.h>" > $@
+      cmd_wrap = \
+	arch=$$(echo $@ | sed -n 's:.*arch/\([^/]*\)/.*:\1:p' | tr a-z A-Z); \
+	upper=$$(echo $*.h | tr a-z A-Z | tr '/.' '__'); \
+	echo "\#ifndef $${arch}_GENERIC_$${upper}" > $@.new; \
+	echo "\#define $${arch}_GENERIC_$${upper}" >> $@.new; \
+	echo "\#include <asm-generic/$*.h>" >> $@.new; \
+	echo "\#endif /* $${arch}_GENERIC_$${upper} */" >> $@.new; \
+	mv -f $@.new $@
 
 quiet_cmd_remove = REMOVE  $(unwanted)
       cmd_remove = rm -f $(unwanted)