Some calls to the argument() function were made twice
because the emit() function didn't know what index to
use for each individual input. I added the function
arguments to the emit() function in order to solve that.

WebGL conformance tests pass.

Change-Id: I548b72cadf7247afd103b6be2ddfeaf39a995025
Reviewed-on: https://swiftshader-review.googlesource.com/4575Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>