go test: incorrect line numbers in compilation errors with -coverprofile flag

[perillo]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 linux/amd64

2. What operating system and processor architecture are you using (go env)?

   GOARCH="amd64"
   GOHOSTARCH="amd64"
   GOHOSTOS="linux"
   GOOS="linux"
   GORACE=""
   GO15VENDOREXPERIMENT="1"
   CC="gcc"
   GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
   CXX="g++"
   CGO_ENABLED="1"
   

3. What did you do?
   When the go test command, with the -coverprofile flag, needs to compile a source file, it reports errors using an incorrect line number.

   The problem can be reproduced running
   $go test -coverprofile=/tmp/out
   with this source file:
   https://play.golang.org/p/WAB6gv-0HC
   and test file:
   https://play.golang.org/p/LCkNJTTOQ1

4. What did you expect to see?

   # test/bug01
   /tmp/go-build602734163/test/bug01/_test/_obj_test/bug.go:6: undefined: fmt.Printz
   FAIL    test/bug01 [build failed]
   

5. What did you see instead?

   # test/bug01
   /tmp/go-build602734163/test/bug01/_test/_obj_test/bug.go:7: undefined: fmt.Printz
   FAIL    test/bug01 [build failed]
   

[perillo]

This is a duplicate of #6329.