fixes for Debian 9

- search for libdwarf.h in new locations (e.g., /usr/include/libdwarf/)
- build Bochs with -std=gnu++98 (gnu++14 is default since GCC 6.1)
- specify "proto2" syntax for protobuf messages
- minor build-system and C++ namespace fixes

Change-Id: I16dbc622c797ef8e936fe3c0fb9b03029d27529d

src/core/comm/DatabaseCampaignMessage.proto.in

@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 import "google/protobuf/descriptor.proto";
 extend google.protobuf.FieldOptions {
     optional bool sql_primary_key = 32382 [ default = false];