Added support for @ in the parser and
replaced all instances of $N.line by
@N.

Change-Id: I7a18278ee0cd5deb90609508abbda2af656daaa4
Reviewed-on: https://swiftshader-review.googlesource.com/3526Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>