The combination of -c and -test.bench causes a hang in go test.
-test.run=does-not-match does not suffer from this.

Running Go tip 18225:9c91baff43a1.

Any go package with tests will reproduce this, e.g.

$ cd $(go env GOROOT)/src/pkg/flag && go test -c -test.bench=does-not-match -x
WORK=/home/tv/tmp/go-build304342983
mkdir -p $WORK/flag/_test/
cd /home/tv/src/go/src/pkg/flag
/home/tv/src/go/pkg/tool/linux_amd64/6g -o $WORK/flag/_test/_go_.6 -p flag -complete -D
_/home/tv/src/go/src/pkg/flag -I $WORK ./flag.go ./export_test.go
/home/tv/src/go/pkg/tool/linux_amd64/pack grcP $WORK $WORK/flag/_test/flag.a
$WORK/flag/_test/_go_.6
/home/tv/src/go/pkg/tool/linux_amd64/6g -o $WORK/flag/_test/_go_.6 -p flag_test
-complete -D _/home/tv/src/go/src/pkg/flag -I $WORK/flag/_test -I $WORK
./example_test.go ./flag_test.go
/home/tv/src/go/pkg/tool/linux_amd64/pack grcP $WORK $WORK/flag/_test/flag_test.a
$WORK/flag/_test/_go_.6
cd $WORK/flag/_test
/home/tv/src/go/pkg/tool/linux_amd64/6g -o ./_go_.6 -p testmain -complete -D
"" -I . -I $WORK ./_testmain.go
/home/tv/src/go/pkg/tool/linux_amd64/pack grcP $WORK ./main.a ./_go_.6
cd .
/home/tv/src/go/pkg/tool/linux_amd64/6l -o $WORK/flag/_test/flag.test -L
$WORK/flag/_test -L $WORK $WORK/flag/_test/main.a


Inspecting $WORK or ps confirms the main.a was created and 6l has exited.