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
+}

ui/build/dumpvars.go

@@ -187,5 +187,6 @@ func runMakeProductConfig(ctx Context, config Config) {
 	config.SetTargetDevice(make_vars["TARGET_DEVICE"])
 	config.SetTargetDeviceDir(make_vars["TARGET_DEVICE_DIR"])
 
+	config.SetPdkBuild(make_vars["TARGET_BUILD_PDK"] == "true")
 	config.SetBuildBrokenDupRules(make_vars["BUILD_BROKEN_DUP_RULES"] != "false")
 }

ui/build/kati.go

@@ -83,6 +83,11 @@ func runKati(ctx Context, config Config) {
 		"-f", "build/make/core/main.mk",
 	}
 
+	// PDK builds still uses a few implicit rules
+	if !config.IsPdkBuild() {
+		args = append(args, "--warn_implicit_rules")
+	}
+
 	if !config.BuildBrokenDupRules() {
 		args = append(args, "--werror_overriding_commands")
 	}