I also added the XCTest file I used, going through every official member according to Apple's Standard Library web pages. You can see that I tried separating the methods that have default implementations to the end of the file. The compilation control is still permitting the code because some of that default code isn't compatible. You can see explanations in the comments of the optional methods that I did not move to the end block (or moved there then moved back before uploading).
Some of the problems were standard library code that assumed the value 1 (or -1) was available. Or that certain unary operations ended up with an output value distinct from the input value. Besides those, the code should work, except for division and open
Range (needed for random).
I already added a new bug based on my discoveries. If you have debug access to the Standard Library, maybe you could find other assumptions (or proof that a zero-width integer is a bad idea).