Only thing I can think of is something blowing up when cross-compiling to a different target because there's no code in the static if branch to handle that arch

Only thing I can think of is something blowing up when cross-compiling to a different target because there's no code in the static if branch to handle that architecture (e.g. stdlib doesn't officially support WASI). But that's not really comptime's fault per se IMHO; you can break things in similar ways in golang, for example. Unlike C, zig's comptime doesn't have grammar altering abilities