misc/cgo/test: pass current environment to syscall.Exec
misc/cgo/test: pass current environment to syscall.Exec

This is needed for typical tests with gccgo, as it passes the
LD_LIBRARY_PATH environment variable to the new program.

Change-Id: I9bf4b0dbdff63f5449c7fcb8124eaeab10ed7f34
Reviewed-on: https://go-review.googlesource.com/35481
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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