Trying building cmake from source

.travis.yml

@@ -133,9 +133,14 @@ before_install:
       sudo pip install -U pytest --ignore-installed six;
     fi
   - if [[ "${TRAVIS_CPU_ARCH}" == "ppc64le" || "${TRAVIS_CPU_ARCH}" == "arm64" ]]; then
-      cmake --version;
-      sudo apt-get install cmake;
-      cmake --version;
+      # The cmake version installed by apt on these architectures is very old,
+      # so build a more recent version from source.
+      wget https://github.com/Kitware/CMake/releases/download/v3.17.1/cmake-3.17.1.tar.gz
+      tar xf cmake-3.17.1.tar.gz
+      cd cmake-3.17.1
+      ./bootstrap
+      make
+      sudo make install
     fi
   #- if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
   #    CMAKE_URL="http://cmake.org/files/v3.7/cmake-3.7.2-Linux-x86_64.tar.gz";