The compiler actually doesn't need any functional changes for this: Sema
does reification based on the tag indices of `std.builtin.Type` already!
So, no zig1.wasm update is necessary.
This change is necessary to disallow name clashes between fields and
decls on a type, which is a prerequisite of #9938.
Fixes regression introduced by 5d5e89aa8d
Turns out since landing that PR we haven't run any tests requiring
symlinks or any Apple SDK on a macOS host. Not great.