cmd/gio: use the import path as basis for the output file

Before this change `go list <pkg>` was used to sanitize the import
path of the package argument. That doesn't work well for building
Go source files directly:

gio -target android helloworld.go

where `go list helloworld.go` simply returns "command-line-arguments".

A better way is to leave the package path alone, and compute the
output file separately from the import path, as reported by
`go list -f {{.ImportPath}} <pkg>`.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

cmd/gio/gio.go

@@ -10,6 +10,7 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 )
 
@@ -24,6 +25,7 @@ var (
 )
 
 type buildInfo struct {
+	name    string
 	pkg     string
 	ldflags string
 	archs   []string
@@ -56,13 +58,15 @@ func main() {
 	default:
 		errorf("invalid -buildmode %s\n", *buildMode)
 	}
-	// Expand relative package paths.
-	pkg, err := runCmd(exec.Command("go", "list", pkg))
+	// Find package name.
+	name, err := runCmd(exec.Command("go", "list", "-f", "{{.ImportPath}}", pkg))
 	if err != nil {
 		errorf("gio: %v", err)
 	}
+	name = filepath.Base(name)
 	bi := &buildInfo{
-		pkg: pkg,
+		name: name,
+		pkg:  pkg,
 	}
 	switch *target {
 	case "js":