The lexer doesn't actually keep the string for literals.

Bug chromium:939239

Change-Id: Ib8b28e75e36d1c6beff8afa580fc4c29c23b6eb0
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/26428Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>