Squashed commit of the following:

commit a90fb13b
Author: Alvin Wong <alvinhochun@gmail.com>
Date:   Sun Sep 10 22:13:45 2017 +0800

    Fix build outside of Windows again

commit 950ef85b
Author: Alvin Wong <alvinhochun@gmail.com>
Date:   Sun Sep 10 22:04:22 2017 +0800

    Fix build outside of Windows

commit 932a2515
Author: Alvin Wong <alvinhochun@gmail.com>
Date:   Sun Sep 10 21:51:23 2017 +0800

    Enable ANGLE and add config options (Windows)

commit 1808e90e
Author: Alvin Wong <alvinhochun@gmail.com>
Date:   Sun Sep 10 01:58:41 2017 +0800

    Add additional Windows OpenGL checking

commit bc059b74
Author: Alvin Wong <alvinhochun@gmail.com>
Date:   Sat Sep 9 22:10:33 2017 +0800

    Refactor OpenGL checking code

commit 58033f21
Merge: 0ee46367 91be09...