ci: extract installing ninja into a script

Author: pietroalbini

src/ci/azure-pipelines/steps/install-windows-build-deps.yml

@@ -105,7 +105,11 @@ steps:
   displayName: Install MinGW
   condition: and(succeeded(), not(variables.SKIP_JOB))
 
-- template: install-windows-build-deps.yml
+- bash: src/ci/scripts/install-ninja.sh
+  env:
+    AGENT_OS: $(Agent.OS)
+  displayName: Install ninja
+  condition: and(succeeded(), not(variables.SKIP_JOB))
 
 # Looks like docker containers have IPv6 disabled by default, so let's turn it
 # on since libstd tests require it

src/ci/azure-pipelines/steps/run.yml

@@ -0,0 +1,16 @@
+#!/bin/bash
+# Note that this is originally from the github releases patch of Ninja
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if isWindows; then
+    mkdir ninja
+    curl -o ninja.zip https://rust-lang-ci-mirrors.s3-us-west-1.amazonaws.com/rustc/2017-03-15-ninja-win.zip
+    7z x -oninja ninja.zip
+    rm ninja.zip
+    ciCommandSetEnv "RUST_CONFIGURE_ARGS" "${RUST_CONFIGURE_ARGS} --enable-ninja"
+    ciCommandAddPath "$(pwd)/ninja"
+fi