Change the compiler's DWARF inline info generation to be more careful
about producing consistent instances of abstract function DIEs. The
new strategy is to insure that the only params/variables created in an
abstract subprogram DIE are those corresponding to declarations in the
original pre-inlining version of the code. If a concrete subprogram
winds up with other vars as part of the compilation process (return
temps, for example, or scalars generated by splitting a structure into
pieces) these are emitted as regular param/variable DIEs instead of
concrete DIEs.

The linker dwarf test now has a couple of new testpoints that include
checks to make sure that all abstract DIE references are
sane/resolvable; this will help catch similar problems in the future.

Fixes #23046.

Change-Id: I9b0030da8673fbb80b7ad50461fcf8c6ac823a37
Reviewed-on: https://go-review.googlesource.com/83675
Run-TryBot: Than McIntosh <thanm@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>