x86, syscall: Allow syscall offset to be symbolic

Allow the specified syscall offset to be symbolic, e.g. a macro.  For
offset system calls, this if nothing else makes the generated code
easier to read.
Suggested-by: NH. J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/r/1321569446-20433-7-git-send-email-hpa@linux.intel.comSigned-off-by: NH. Peter Anvin <hpa@linux.intel.com>

arch/x86/syscalls/syscallhdr.sh

@@ -15,7 +15,11 @@ grep -E "^[0-9A-Fa-fXx]+[[:space:]]+${my_abis}" "$in" | sort -n | (
     echo ""
 
     while read nr abi name entry ; do
-	echo "#define __NR_${prefix}${name}" $((nr+offset))
+	if [ -z "$offset" ]; then
+	    echo "#define __NR_${prefix}${name} $nr"
+	else
+	    echo "#define __NR_${prefix}${name} ($offset + $nr)"
+        fi
     done
 
     echo ""