[Issue 13717] `split` no longer defined by std.string

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13717

--- Comment #1 from hst...@quickfur.ath.cx ---
Failing test case:
------
import std.string;
void main () {
    foreach (s; "ab cd ef".split) {}
}
------

Compiles with Phobos commit c0028b4, but fails starting with ab83cd94.

--