Remove Ubuntu Xenial from CI. (#1833)

Ubuntu 16.04 has reached end of standard support.

Signed-off-by: Wolfgang Hess <[email protected]>

Author: wohe

.travis.yml

@@ -22,7 +22,6 @@ cache:
     - /home/travis/docker/
 
 env:
-  - LSB_RELEASE=xenial DOCKER_CACHE_FILE=/home/travis/docker/xenial-cache.tar.gz CC=gcc CXX=g++
   - LSB_RELEASE=bionic DOCKER_CACHE_FILE=/home/travis/docker/bionic-cache.tar.gz CC=gcc CXX=g++
   - LSB_RELEASE=focal DOCKER_CACHE_FILE=/home/travis/docker/focal-cache.tar.gz CC=gcc CXX=g++
   - LSB_RELEASE=stretch DOCKER_CACHE_FILE=/home/travis/docker/stretch-cache.tar.gz CC=gcc CXX=g++

Dockerfile.xenial

@@ -78,10 +78,6 @@ macro(google_initialize_cartographer_project)
   else()
     set(GOOG_CXX_FLAGS "-pthread -fPIC ${GOOG_CXX_FLAGS}")
 
-    if (CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 6.1)
-      google_add_flag(GOOG_CXX_FLAGS "-std=c++11")
-    endif()
-
     google_add_flag(GOOG_CXX_FLAGS "-Wall")
     google_add_flag(GOOG_CXX_FLAGS "-Wpedantic")
 

cmake/functions.cmake

@@ -65,7 +65,7 @@ Getting started without ROS
 Please see our ROS integration as a starting point for integrating your system
 with the standalone library. Currently, it is the best available reference.
 
-On Ubuntu 16.04 (Xenial):
+On Ubuntu 18.04 (Bionic):
 
 .. literalinclude:: ../../scripts/install_debs_cmake.sh
   :language: bash
@@ -97,8 +97,8 @@ on systems that meet the following requirements:
 
 * 64-bit, modern CPU (e.g. 3rd generation i7)
 * 16 GB RAM
-* Ubuntu 16.04 (Xenial), 18.04 (Bionic), 20.04 (Focal)
-* gcc version 4.8.4, 5.4.0, 7.5.0, 9.3.0
+* Ubuntu 18.04 (Bionic), 20.04 (Focal)
+* gcc version 6.3.0, 7.5.0, 9.3.0
 
 Known Issues
 ------------