Don't special-case `builtin` too much
Don't special-case `builtin` too much

Let's use the usual declaration-searching mechanism that resolves the
`usingnamespace` declarations on the go instead of directly peeking into
the symbol table.

Fixes #4134

raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig