test: add test for gccgo issue #15722
test: add test for gccgo issue #15722

Change-Id: I4faf9a55414e217f0c48528efb13ab8fdcd9bb16
Reviewed-on: https://go-review.googlesource.com/24845
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

suncycheng/go,goodlang/good,codestation/go,CAFxX/go,ImJasonH/go,suncycheng/go,akutz/go,momchil-velikov/go,vsekhar/elastic-go,momchil-velikov/go,golang/go,Cofyc/go,vsekhar/elastic-go,polyverse-security/go,derekmarcotte/go,polyverse-security/go,momchil-velikov/go,suncycheng/go,linux-on-ibm-z/go,vsekhar/elastic-go,cloudflare/go,akutz/go,cloudflare/go,suncycheng/go,josharian/go,cloudflare/go,linux-on-ibm-z/go,josharian/go,polyverse-security/go,nawawi/go,nawawi/go,nawawi/go,linux-on-ibm-z/go,codestation/go,nawawi/go,codestation/go,linux-on-ibm-z/go,ImJasonH/go,codestation/go,CAFxX/go,josharian/go,CAFxX/go,codestation/go,goodlang/good,momchil-velikov/go,cloudflare/go,derekmarcotte/go,goodlang/good,vsekhar/elastic-go,nawawi/go,derekmarcotte/go,CAFxX/go,ImJasonH/go,polyverse-security/go,ImJasonH/go,suncycheng/go,christopher-henderson/Go,golang/go,linux-on-ibm-z/go,golang/go,vsekhar/elastic-go,codestation/go,vsekhar/elastic-go,goodlang/good,linux-on-ibm-z/go,cloudflare/go,akutz/go,codestation/go,Cofyc/go,ImJasonH/go,golang/go,suncycheng/go,polyverse-security/go,momchil-velikov/go,cloudflare/go,akutz/go,vsekhar/elastic-go,derekmarcotte/go,derekmarcotte/go,josharian/go,CAFxX/go,polyverse-security/go,suncycheng/go,akutz/go,akutz/go,golang/go,suncycheng/go,golang/go,golang/go,CAFxX/go,derekmarcotte/go,josharian/go,Cofyc/go,Cofyc/go,momchil-velikov/go,nawawi/go,Cofyc/go,codestation/go,nawawi/go,ImJasonH/go,josharian/go,akutz/go,akutz/go,polyverse-security/go,derekmarcotte/go,golang/go,linux-on-ibm-z/go,Cofyc/go,ImJasonH/go,derekmarcotte/go,josharian/go,goodlang/good,vsekhar/elastic-go,Cofyc/go,ImJasonH/go,Cofyc/go,momchil-velikov/go,CAFxX/go,CAFxX/go,nawawi/go,goodlang/good,cloudflare/go,polyverse-security/go,cloudflare/go,linux-on-ibm-z/go,momchil-velikov/go,goodlang/good,josharian/go,goodlang/good