Fix Cirrus build: use python3 (#3726)

Author: JohanEngelen

.cirrus.yml

@@ -1,12 +1,8 @@
-# Installs pip and lit, clones the git submodules, builds LDC and the test
+# Installs lit, clones the git submodules, builds LDC and the test
 # runners and runs the tests.
 # Requires env variables EXTRA_CMAKE_FLAGS and PARALLELISM.
 common_steps_template: &COMMON_STEPS_TEMPLATE
-  install_pip_and_lit_script: |
-    # Install pip
-    curl --max-time 300 --retry 3 -OL https://bootstrap.pypa.io/pip/2.7/get-pip.py
-    python get-pip.py --user
-    rm get-pip.py
+  install_lit_script: |
     # Install lit
     python -m pip install --user lit
     python -c "import lit.main; lit.main.main();" --version . | head -n 1
@@ -71,8 +67,11 @@ install_ubuntu_prerequisites_template: &INSTALL_UBUNTU_PREREQUISITES_TEMPLATE
     apt-get -yq install \
       git-core cmake ninja-build $gcc_pkg \
       llvm-dev zlib1g-dev libclang-common-$LIBCLANG_COMMON_VERSION-dev \
-      $libcurl_pkg curl gdb python tzdata unzip zip \
+      $libcurl_pkg curl gdb python3 python3-pip tzdata unzip zip \
       $EXTRA_APT_PACKAGES
+    python3 --version
+    ln -s $(which python3) /usr/bin/python
+    python --version
     # Download & extract host LDC
     curl --max-time 300 --retry 3 -L -o ldc2.tar.xz https://github.com/ldc-developers/ldc/releases/download/v$HOST_LDC_VERSION/ldc2-$HOST_LDC_VERSION-linux-x86_64.tar.xz
     mkdir host-ldc
@@ -105,6 +104,10 @@ install_macos_prerequisites_template: &INSTALL_MACOS_PREREQUISITES_TEMPLATE
     mkdir host-ldc
     tar -xf ldc2.tar.xz --strip 1 -C host-ldc
     rm ldc2.tar.xz
+    # Install Python3
+    brew install python
+    ln -sf $(which python3) /usr/local/bin/python
+    python --version
 
 environment:
   CIRRUS_CLONE_DEPTH: 50
@@ -155,11 +158,13 @@ task:
     OS: osx
     PATH: ${CIRRUS_WORKING_DIR}/../cmake/bin:${CIRRUS_WORKING_DIR}/../ninja:${CIRRUS_WORKING_DIR}/../llvm/bin:${PATH}
     PARALLELISM: 12
-    matrix:
-      - TASK_NAME_SUFFIX: x64
-        EXTRA_CMAKE_FLAGS: "-DBUILD_LTO_LIBS=ON"
-      - TASK_NAME_SUFFIX: x64 shared-libs-only
-        EXTRA_CMAKE_FLAGS: "-DBUILD_LTO_LIBS=ON -DBUILD_SHARED_LIBS=ON"
+  brew_cache:
+    folder: "$HOME/Library/Caches/Homebrew"
+  matrix:
+    - TASK_NAME_SUFFIX: x64
+      EXTRA_CMAKE_FLAGS: "-DBUILD_LTO_LIBS=ON"
+    - TASK_NAME_SUFFIX: x64 shared-libs-only
+      EXTRA_CMAKE_FLAGS: "-DBUILD_LTO_LIBS=ON -DBUILD_SHARED_LIBS=ON"
   << : *INSTALL_MACOS_PREREQUISITES_TEMPLATE
   << : *COMMON_STEPS_TEMPLATE
 
@@ -181,6 +186,8 @@ task:
     cd $CIRRUS_WORKING_DIR/..
     sysctl -n hw.ncpu
     pkg install -y git cmake ninja gmake llvm bash gtar p7zip
+    python --version
+    python -m ensurepip
     # Download & extract host LDC
     curl --max-time 300 --retry 3 -L -o ldc2.tar.xz https://github.com/ldc-developers/ldc/releases/download/v$HOST_LDC_VERSION/ldc2-$HOST_LDC_VERSION-freebsd-x86_64.tar.xz
     mkdir pre-ldc