Build: Verify checksums when downloading PhantomJS (#20558)

* Build: Supply curl -f when downloading phantomjs
* Build: Verify checksums of downloaded PhantomJS zips

scripts/build/download-phantomjs.sh

-#!/bin/bash -e
+#!/bin/bash
+set -eo pipefail
 
 if [ ! -d '/tmp/phantomjs' ]; then
   _version="2.1.1"
 
-  curl -L https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-$_version-windows.zip > /tmp/phantomjs-win.zip
-  curl -L https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-$_version-macosx.zip > /tmp/phantomjs-mac.zip
+  curl -fL https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-$_version-windows.zip -o /tmp/phantomjs-win.zip
+  [ "$(sha256sum /tmp/phantomjs-win.zip | cut -d' ' -f1)" = \
+    "d9fb05623d6b26d3654d008eab3adafd1f6350433dfd16138c46161f42c7dcc8" ] || \
+    (echo "Checksum mismatch phantomjs-$_version-windows.zip"; exit 1)
+  curl -fL https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-$_version-macosx.zip -o /tmp/phantomjs-mac.zip
+  [ "$(sha256sum /tmp/phantomjs-mac.zip | cut -d' ' -f1)" = \
+    "538cf488219ab27e309eafc629e2bcee9976990fe90b1ec334f541779150f8c1" ] || \
+    (echo "Checksum mismatch phantomjs-$_version-mac.zip"; exit 1)
 
   cd /tmp
   unzip /tmp/phantomjs-win.zip