Best way to fix gate post over foundation that extends
It's very common where I come from (New Zealand) to Dynabolt the gate or fence post directly to a brick, block or rendered wall.
I have about 4 of them in various places around my 1960's render over concrete block house
As long as the size of the Dynabolt is appropriate there should be no significant weakening of the brick(s) you drill into. There are variations of these Dynabolts that are chem-set into the wall/brick/block with Epoxy, one of these would in theory further reduce any negliable impact in the integrity of the brick.