DLLImportRelocation pass doesn't support GEPs

[kinke]

It's currently limited to initializers referencing either a dllimport global directly, or a cast one. For

void foo() {
    import std.variant;
    auto t = typeid(VariantN!16);
}

the generated TypeInfo_Struct uses a GEP:

@_D42TypeInfo_S3std7variant__T8VariantNVmi16ZQp6__initZ = linkonce_odr global %object.TypeInfo_Struct { …, { i64, i8* } { i64 24, i8* getelementptr inbounds (%"std.variant.VariantN!16LU.VariantN", %"std.variant.VariantN!16LU.VariantN"* @_D3std7variant__T8VariantNVmi16ZQp6__initZ, i32 0, i32 0, i32 0) }, …
…
@_D3std7variant__T8VariantNVmi16ZQp6__initZ = external dllimport constant %"std.variant.VariantN!16LU.VariantN", align 8 ; [#uses = 1]