[dev.link] cmd/link: refactor DWARF fn die processing to remove name lookups
Rework the code in the linker that visits DWARF subprorgam DIEs to
reduce number of symbol name instantiations and name lookups, by
making better use of relocation target symbol types.
Change-Id: Ifb2a4e24874b8c891d7fdf17dd749c3f9139157a
Reviewed-on: https://go-review.googlesource.com/c/go/+/234685
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Jeremy Faller <jeremy@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com>