Turn implicit rules into warnings

Test: build_test in downstream branches
Change-Id: I853e3fa11793cc76ad568b74f7dc31c3d1c5582b

ui/build/config.go

@@ -50,6 +50,7 @@ type configImpl struct {
 	targetDevice    string
 	targetDeviceDir string
 
+	pdkBuild       bool
 	brokenDupRules bool
 
 	pathReplaced bool
@@ -579,3 +580,11 @@ func (c *configImpl) SetTargetDeviceDir(dir string) {
 func (c *configImpl) TargetDeviceDir() string {
 	return c.targetDeviceDir
 }
+
+func (c *configImpl) SetPdkBuild(pdk bool) {
+	c.pdkBuild = pdk
+}
+
+func (c *configImpl) IsPdkBuild() bool {
+	return c.pdkBuild
+}