Make it possible to debug soong_ui.

This works by setting the SOONG_UI_DELVE= environment variable to the
port on which soong_ui should accept a Delve connection on.

This is achieved by reusing the Delve execution logic between soong_ui
and soong_build.

Test: Manual.
Change-Id: Id2c1d4b6faac1a4a3918c91030ce2239f7daf54f
diff --git a/cmd/soong_ui/main.go b/cmd/soong_ui/main.go
index 74ede68..1c5e78a 100644
--- a/cmd/soong_ui/main.go
+++ b/cmd/soong_ui/main.go
@@ -25,6 +25,7 @@
 	"strings"
 	"time"
 
+	"android/soong/shared"
 	"android/soong/ui/build"
 	"android/soong/ui/logger"
 	"android/soong/ui/metrics"
@@ -118,6 +119,8 @@
 // Command is the type of soong_ui execution. Only one type of
 // execution is specified. The args are specific to the command.
 func main() {
+	shared.ReexecWithDelveMaybe(os.Getenv("SOONG_UI_DELVE"), shared.ResolveDelveBinary())
+
 	buildStarted := time.Now()
 
 	c, args, err := getCommand(os.Args)