cmd/addr2line: use the test binary as 'addr2line' instead of rebuilding it twice
cmd/addr2line: use the test binary as 'addr2line' instead of rebuilding it twice

This not only reduces the latency of the test, but also respects
build flags like '-race' and '-cover' passed to the 'go test' command.

Change-Id: Ie9a3c03d32d7eea268ba6f8f8ac4000539434052
Reviewed-on: https://go-review.googlesource.com/c/go/+/450713
Auto-Submit: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go