Regression from 2.050 to 2.051 (Linux).

When compiling with -gc -c, the testcase below will cause 2.051 to segv.
File compiles OK on 2.050.
File also compiles just fine (even on 2.051) if -gc is omitted.
DMD produces expected link errors if you compile with only -gc argument.

The key issues appear to be:
  - The foreach loop inside the function.
  - The parent pointer in Foo must be *BOTH* const and a pointer to its own
    type.  If you make it non-const, or a pointer to something else, it works.

TESTCASE:

void DMD_BUG_WORKAROUND()  // issue 3770
{
  /* if you don't have a dummy function like this in the module where a type
   * was declared, then dmd won't give it to you when you use it in an
   * associative array elsewhere, and you'll get link errors.
   */
  Foo    tmp;
  string dummy;

  foreach(name; tmp.table.keys)
    dummy ~= name;
}

struct Foo
{
  const(Foo)       *parent;
  FooElem*[string]  table;
};

struct FooElem
{
};