--- a/configure	Tue Apr 25 01:35:13 2017 +0200
+++ b/configure	Tue Apr 25 21:46:46 2017 +0200
@@ -297,6 +297,9 @@
    --cflags)
       CFLAGS="$value"
       ;;
+   --add-cflags)
+      CFLAGS="$CFLAGS $value"
+      ;;
    --ldflags)
       LDFLAGS="$value"
       ;;