Some virtual functions with common names had different signature,
which generates warnings. These functions didn't need to be virtual,
so they are no longer virtual in order to fix the warnings.

Change-Id: I4d8f5a9fdb3f4f520efe1aea0ce5d179b519bf8b
Reviewed-on: https://swiftshader-review.googlesource.com/5461Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>