func Build(packagePath string, args ...string) (compiledPath string, err error) {
	return doBuild(os.Getenv("GOPATH"), packagePath, nil, args...)
}
/*
Build uses go build to compile the package at packagePath.  The resulting binary is saved off in a temporary directory.
A path pointing to this binary is returned.

Build uses the $GOPATH set in your environment.  It passes the variadic args on to `go build`.
package gexec
import (
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"runtime"
	"sync"
)
var (
	mu     sync.Mutex
	tmpDir string
)