Issue 7230 - Crash during printing anonymous union with writeln family functions.

[9rnsr]

http://d.puremagic.com/issues/show_bug.cgi?id=7230

Format struct that has anonymous union fields, they overlapp each otther:

struct S {
  Field1 field0;
  union {
    Field2 field2;
    Field3 field3;
  }
  Field4 field4;
}

is formatted like follows:

S(field0, #{overlap field_ov_1, field_ov_2}, field_4)

This is much special case, and the formatting is debatable thing.