Pass target_name as --binname to gobuild.py.

This allows the output binary to be named differently than the go
package.

Change-Id: I612b77e4cf28c0ddf56b32cb32ad0e0f2e8b772e
diff --git a/go/go_binary.gni b/go/go_binary.gni
index c75ea94..b6e94af 100644
--- a/go/go_binary.gni
+++ b/go/go_binary.gni
@@ -31,6 +31,8 @@
       current_cpu,
       "--go-tool",
       rebase_path("//buildtools/go"),
+      "--binname",
+      rebase_path("$out_path"),
       invoker.gopackage,
     ]