Emit some type declarations in .gdb_index

Emit some type declarations in .gdb_index

If you run struct-decl.exp with the .gdb_index board, you will see
that "the_type" is not emitted in the index.  This would cause a
failure in this series.  The fix is to ensure that certain necessary
type declarations are emitted.

However, a naive fix here will regress stub-array-size.exp, where a
type declaration and a type definition are both seen -- but the
declaration is seen first and causes a failure.  This is handled by
adding some code (including a mild hack) to filter out type
declarations when a corresponding type definition is seen.

Acked-By: Simon Marchi <simon.marchi@efficios.com>