MAKEALL: Use POSIX math

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/MAKEALL b/MAKEALL
index 4688d42..dbcad87 100755
--- a/MAKEALL
+++ b/MAKEALL
@@ -9,7 +9,7 @@
 
 if [ "$BUILD_NCPUS" -gt 1 ]
 then
-	JOBS=-j`expr "$BUILD_NCPUS" + 1`
+	JOBS="-j $((BUILD_NCPUS + 1))"
 else
 	JOBS=""
 fi