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.
This introduces the new test step `test-c-import`, and removes the
ability of the behavior tests to `@cImport` paths relative to `test`.
This allows the behavior tests to be run without translate c.
