Insignificant

Had the Confederacy won the battle at Gettysburg, I don’t believe the outcome of the war would have changed. The only reason why Gettysburg is so well known is because it was the turning point of the war. If the South had won, Gettysburg would be just another random victory for the South, adding to their list of wins. The Union, at that point, was not doing so well, so another loss would be just another random loss. There would have probably been another different turning point later in the war if the Union had lost, because they were better suited for a longer war.

France and Britain would not have joined the Confederacy even if they had won at Gettysburg. The South was already doing pretty well before Gettysburg, yet the European countries never joined forces. They already have their own sources of cotton, like from India, so the South having cotton would not convince them to join. Also, France and Britain had already abolished slavery, so they would not see any reason or motivation to join the Confederacy. 

Lincoln would not really have changed his mindset about the war. He is already determined to win this war, and will stop at nothing to seize the victory. This can be shown with the Emancipation Proclamation, which showed that he really would do what he could for the war. He had not given up before Gettysburg, where the Union was losing, so I don't think another loss would have much effect on Lincoln. 

Basically, if the Confederacy had won at Gettysburg, it would not be significant, and not as well known as it is today. It would just be a minor battle, not changing the outcome of the war nor the situation of both sides.