avoid generating empty if/else blocks on autoconf 2.63, fixes #3684

diff --git a/m4/pdns_with_protobuf.m4 b/m4/pdns_with_protobuf.m4
index 39d4e1c96935710b2523f7311d4cfac79cd477fe..f106c5889fde51d1d9312930e85f2d9d080a6790 100644 (file)
--- a/m4/pdns_with_protobuf.m4
+++ b/m4/pdns_with_protobuf.m4
@@ -9,7 +9,7 @@ AC_DEFUN([PDNS_WITH_PROTOBUF], [
 
   AS_IF([test "x$with_protobuf" != "xno"], [
     AS_IF([test "x$with_protobuf" = "xyes" -o "x$with_protobuf" = "xauto"], [
-      PKG_CHECK_MODULES([PROTOBUF], [protobuf], [ ], [ ])
+      PKG_CHECK_MODULES([PROTOBUF], [protobuf], [ : ], [ : ])
       AC_CHECK_PROG([PROTOC], [protoc], [protoc])
     ])
   ])