Add config.h in files were it was missing

Related to https://github.com/profanity-im/profanity/issues/1512

src/otr/otr.c

@@ -33,6 +33,8 @@
  *
  */
 
+#include "config.h"
+
 #include <libotr/proto.h>
 #include <libotr/privkey.h>
 #include <libotr/message.h>

src/otr/otrlibv3.c

@@ -32,6 +32,8 @@
  * source files in the program, then also delete it here.
  *
  */
+#include "config.h"
+
 #include <libotr/proto.h>
 #include <libotr/privkey.h>
 #include <libotr/message.h>

src/otr/otrlibv4.c

@@ -33,6 +33,8 @@
  *
  */
 
+#include "config.h"
+
 #include <libotr/proto.h>
 #include <libotr/privkey.h>
 #include <libotr/message.h>