Compiling on IBM System Z fails with "Unsupported platform" and other errors

When building MariaDB on IBM System Z, builds fail with various errors, including "Unsupported platform"

See the following build logs:

• http://buildbot.askmonty.org/buildbot/builders/ibmz-sles11-bintar/builds/2/steps/compile/logs/stdio
• http://buildbot.askmonty.org/buildbot/builders/ibmz-rhel6-bintar/builds/1/steps/compile/logs/stdio

This bug report appears to be related: https://bugs.mysql.com/bug.php?id=78687