cmd/compile: allow duplicate DWARF producer symbols
cmd/compile: allow duplicate DWARF producer symbols

When building test binaries, we build one archive with all of the test
sources and a second archive with the generated test package main and
link them together. If the test sources are themselves in package main
and the test was compiled with non-default compiler flags, then both
archives will contain a go.cuinfo.producer.main symbol, leading to a
duplicate symbol failure.

This has been causing test build failures on darwin-arm-a1428ios,
darwin-arm64-a1549ios, linux-amd64-noopt, android-arm-wiko-fever, and
android-arm64-wiko-fever since CL 71430 added this symbol. This CL
should fix the build.

Change-Id: I69051c846e7c0d97395a865a361cae07f411f9ad
Reviewed-on: https://go-review.googlesource.com/71771
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

christopher-henderson/Go,cloudflare/go,cloudflare/go,codestation/go,Cofyc/go,CAFxX/go,nawawi/go,akutz/go,golang/go,golang/go,golang/go,nawawi/go,josharian/go,Cofyc/go,josharian/go,CAFxX/go,akutz/go,codestation/go,codestation/go,akutz/go,codestation/go,CAFxX/go,akutz/go,Cofyc/go,golang/go,CAFxX/go,CAFxX/go,golang/go,golang/go,josharian/go,cloudflare/go,akutz/go,akutz/go,Cofyc/go,akutz/go,josharian/go,nawawi/go,nawawi/go,cloudflare/go,Cofyc/go,josharian/go,CAFxX/go,cloudflare/go,Cofyc/go,Cofyc/go,akutz/go,cloudflare/go,josharian/go,codestation/go,golang/go,nawawi/go,josharian/go,CAFxX/go,nawawi/go,codestation/go,CAFxX/go,cloudflare/go,nawawi/go,golang/go,codestation/go,cloudflare/go,nawawi/go,codestation/go,josharian/go,Cofyc/go