Merge bitcoin#15276: travis: Compile once on trusty

fa5ce3f travis: Compile trusty with depends for now (MarcoFalke)
fa83999 travis: Compile once on trusty (MarcoFalke)

Pull request description:

  To avoid accidentally regressing again on bitcoin#15172, we should compile at least once with gcc4.8 (the minimum required version)

  Note that this uses the trusty image, which will be removed in a few months from the docker hub, so in the future it had to be switched to the centos7 (or similar) image, which should come with gcc4.8 as well.

Tree-SHA512: 9d1704464bde8dbaf3319ac35f72d32dce549818730d3b2fb63df817f84a88dd64aa3419b97a57c1120ffb254784503b7d2675b1291d4ed073cd2a2488aa717d

.travis.yml

@@ -256,6 +256,16 @@ after_success:
         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\""
+    - stage: test
+      name: 'x86_64 Linux  [GOAL: install]  [trusty]  [depends for now]'
+      env: >-
+        HOST=x86_64-unknown-linux-gnu
+        DOCKER_NAME_TAG=ubuntu:14.04
+        PACKAGES="python3-zmq qtbase5-dev qttools5-dev-tools libicu-dev libpng-dev libssl-dev libevent-dev bsdmainutils libboost-system-dev libboost-filesystem-dev libboost-chrono-dev libboost-test-dev libboost-thread-dev libdb5.1++-dev libminiupnpc-dev libzmq3-dev libprotobuf-dev protobuf-compiler libqrencode-dev"
+        RUN_FUNCTIONAL_TESTS=false
+        GOAL="install"
+        BITCOIN_CONFIG="--enable-zmq --with-incompatible-bdb --with-gui=no"
+
     - stage: test
       name: 'x86_64 Linux  [GOAL: install]  [xenial]  [no depends, only system libs, sanitizers: thread (TSan), no wallet]'
       env: >-