[pebers]

If people have done architecture-specific things they may not compile (or worse, crash inexplicably at runtime).

I tried doing more or less that (compiling a C++ Windows app for 64-bit) a few jobs ago and eventually discovered that way down in a library somewhere a dev (who had long since departed) did some trickery in string processing routines that relied on arguments being lined up on the stack, which is no longer the case with the x86_64 calling convention. That remains the worst piece of code I've ever worked with - it's innocuous to look at, and any developer who understands why that works should also have known better than to do it.

More generally, integer size issues can arise - if `int` remains 32 bits it's no longer enough to capture the difference between two pointers (and obviously should never have been used for that, but often these things happen).