This cl simply adds the function signatures,
without any implementation, for the new
GLES 3.0 builtin functions.

Change-Id: Ib67830aedd3c067ca7c16738e4a071547a893321
Reviewed-on: https://swiftshader-review.googlesource.com/2860Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>