emulator/opengl: Fix Windows SDK build.

This patch fixes the Windows SDK build. A previous patch
apparently broke it even though I could not reproduce this
locally before submitting.

What it does is, when using the platform build to generate
Windows binaries, use the host Linux binary instead of rebuilding
the 'emugen' tool from sources.

Note that the emulator's standalone build supports building
host Linux binaries even when targetting Windows by default.

+ Add a missing module import that got lost in translation
  for some odd reason.

Change-Id: I2ccd962d8b3df859b2cba82573225820b69b0d32
2 files changed