Currently, the following two codes generate the identical dwarf info
for type Foo.

prog 1)
type Foo struct {
   Bar
}

prog 2)
type Foo struct {
   Bar Bar
}

This change adds a go-specific attribute DW_AT_go_embedded_field
to annotate each member entry. Its absence or false value indicates
the corresponding member is not an embedded field.

Update #20037

Change-Id: Ibcbd2714f3e4d97c7b523d7398f29ab2301cc897
Reviewed-on: https://go-review.googlesource.com/41873Reviewed-by: David Chase <drchase@google.com>