[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 hsteoh at quickfur.ath.cx ---
Failing test case:
------
import std.string;
void main () {
    foreach (s; "ab cd ef".split) {}
}
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Compiles with Phobos commit c0028b4, but fails starting with ab83cd94.

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