OpenGL ES 3.0 entry functions are exported in the exports.map version script,
but the source file defining them was not being compiled (ES3 support is still
disabled).

Change-Id: I5e42082304beb2b37de2bcc7ffcf3b2fc65ecc7d
Reviewed-on: https://swiftshader-review.googlesource.com/4732Reviewed-by: Keun Soo Yim <yim@google.com>
Reviewed-by: Greg Hartman <ghartman@google.com>
Tested-by: Keun Soo Yim <yim@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>