Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.8.3 windows/amd64

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

set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\xwang24\Documents\goWorkspace
set GORACE=
set GOROOT=C:\Go
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0
set CXX=g++
set CGO_ENABLED=1
set PKG_CONFIG=pkg-config
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2

What did you do?

I have two packages:
src/github.com/user1/hello/hello.go
src/github.com/user2/hello/hello.go
After the first hello.go is installed, hello.exe is generated under bin/,
then after the second hello.go is installed, hello.exe generated by the previous one is overridden.

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

What did you expect to see?

the generated exe should be under bin/package info.
For example,
bin/github.com/user1/hello/hello.exe

What did you see instead?

bin/hello.exe