Pass the target GLSL version to InitBuiltInFunctionEmulatorForGLSL so that
it can be updated to generate emulated functions for multiple versions.

BUG=angleproject:1044

Change-Id: I34c408df52fd0f7d6c2f66d0579ac854afd93b87
Reviewed-on: https://chromium-review.googlesource.com/277700Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>