Gnostic Gospels

In the gospel of Thomas is found the following perversion of a Messianic prophecy from Psalm 118

From the gospel of Thomas - http://www.gnosis.org/naghamm/gthlamb.html
(66) Jesus said, "Show me the stone which the builders have rejected. That one is the cornerstone."

In all three true gospels, Jesus is quoting directly from the scriptures in Mt 21:42, Mr 12:10, Lu 20:17. Peter, filled with the Holy Spirit, identified who this was “[ Jesus Christ of Nazareth] is the ‘stone which was rejected by you builders, which has become the chief cornerstone.’
Paul in Ephesians identifies the stone that the builders rejected..."having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone."

So if Jesus was quoting from the Tonakh, which has been proven to be accurate and unchanged, then how could Constantine have changed the text in the true gospels to mean something else? Looks like the real distorted text is the gnostic Thomas gospel.