djgpp does have strdup().

ares/Makefile.dj

@@ -28,7 +28,7 @@ CFLAGS += -DWATT32 -DHAVE_AF_INET6 -DHAVE_PF_INET6 -DHAVE_IOCTLSOCKET \
           -DRECVFROM_TYPE_ARG3='int' -DRECVFROM_TYPE_ARG4='int' \
           -DRECVFROM_TYPE_ARG6='int' -DRECVFROM_TYPE_RETV='int' \
           -DRECVFROM_TYPE_ARG5='struct sockaddr' -DHAVE_RECVFROM \
-          -DRECVFROM_TYPE_ARG2_IS_VOID
+          -DRECVFROM_TYPE_ARG2_IS_VOID -DHAVE_STRDUP
 
 LDFLAGS = -s