travis: Compile once on xenial

.travis.yml

@@ -99,6 +99,15 @@ jobs:
         DEP_OPTS="NO_QT=1 NO_UPNP=1 DEBUG=1 ALLOW_HOST_PACKAGES=1"
         GOAL="install"
         BITCOIN_CONFIG="--enable-zmq --with-gui=qt5 --enable-glibc-back-compat --enable-reduce-exports --enable-debug CXXFLAGS=\"-g0 -O2\""
+# x86_64 Linux (xenial, no depends, only system libs)
+    - stage: test
+      env: >-
+        HOST=x86_64-unknown-linux-gnu
+        DOCKER_NAME_TAG=ubuntu:16.04
+        PACKAGES="python3-zmq qtbase5-dev qttools5-dev-tools libssl-dev libevent-dev bsdmainutils libboost-system-dev libboost-filesystem-dev libboost-chrono-dev libboost-test-dev libboost-thread-dev libdb5.3++-dev libminiupnpc-dev libzmq3-dev libprotobuf-dev protobuf-compiler libqrencode-dev"
+        NO_DEPENDS=1
+        GOAL="install"
+        BITCOIN_CONFIG="--enable-zmq --with-incompatible-bdb --enable-glibc-back-compat --enable-reduce-exports --with-gui=qt5 CPPFLAGS=-DDEBUG_LOCKORDER"
 # x86_64 Linux (no depends, only system libs)
     - stage: test
       env: >-