1. src/common/platform.h updated to define ANGLE_PLATFORM_POSIX on Haiku.
2. include/EGL/eglplatform.h updated to add stubs typedefs for
platform-specific primitives for Haiku.

Change-Id: I28775e909ad9cabec1c474ff4fe0a241eb05d6a1
Reviewed-on: https://chromium-review.googlesource.com/573022
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>