Fix consistent crash on OS X when rendering to PDF format.

By implementing a dummy platform native interface (for now, it may be
extended in the near future), QPlatformPrinterSupportPlugin will avoid
the path of loading the printer support plugin
(QCocoaPrinterSupportPlugin on OS X).

Related upstream bug (QCocoaPrinterSupportPlugin problem with static build):
https://bugreports.qt-project.org/browse/QTBUG-33109

https://github.com/ariya/phantomjs/issues/12500
Port the tests of 'system' module.

https://github.com/ariya/phantomjs/issues/12439
Improve handling of crash dumps (issue #12236).

 * If the environment variable PHANTOMJS_DISABLE_CRASH_DUMPS
   is set to any value, do not initialize Breakpad.

 * On Mac and Linux, if the environment variable TMPDIR is set,
   put the crash dumps there instead of in /tmp.

 * On Windows, %TEMP% was already being honored, but streamline
   the code for that.

 * Move the code that initializes Breakpad, and the code to print
   the crash messages, to their own module (src/crashdump.{h,cpp})
   and RAII class (CrashHandler).

 * Better wording of the crash message, particularly in the case where
   Breakpad failed to write a minidump file; update URL of crash-reporting
   guide.

 * Generally less repetitive code.  (Still way too many #ifdefs.)
Convert Utils into a namespace and remove dead code.

Post-cleanup for #12236.