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/jsbuild.go

@@ -13,7 +13,7 @@ import (
 func buildJS(bi *buildInfo) error {
 	out := *destPath
 	if out == "" {
-		out = filepath.Base(bi.pkg)
+		out = bi.name
 	}
 	if err := os.MkdirAll(out, 0700); err != nil {
 		return err