cmd/compile: fix regression in DWARF inlined routine variable tracking

cmd/compile: fix regression in DWARF inlined routine variable tracking

Fix a bug in the code that generates the pre-inlined variable
declaration table used as raw material for emitting DWARF inline
routine records. The fix for issue 23704 altered the recipe for
assigning file/line/col to variables in one part of the compiler, but
didn't update a similar recipe in the code for variable tracking.
Added a new test that should catch problems of a similar nature.

Fixes #24460.

Change-Id: I255c036637f4151aa579c0e21d123fd413724d61
Reviewed-on: https://go-review.googlesource.com/101676
Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>