Run all of Xcode's "Fix-it"s at once

There is actually a solution for this in Xcode 7.2¹'s Editor menu.

This is the shortcut:

⌃+⌥+⌘+f

which is

ctrl+alt+cmd+f

¹ This is the version I can confirm, might work in earlier versions as well.

XCode's "fix-it" isn't always reliable enough to make the changes that the code needs to run properly. Even if there was such a button, I wouldn't advise using it. The only thing I can think of to make it quicker to go through is to use: Navigate > Jump to Next Issue which would mean you wouldn't have to comb through the code to find all of the errors, Xcode would take you straight to them.

Fix All Issues button in Xcode 10.3