Always run Soong

Without switching on USE_SOONG, this lets us verify that all builds have
blueprint/soong/go, and can generate a build.ninja file without
producing errors.

Change-Id: I79451ce24c8b5b6745e41d951153265441c33e8a
diff --git a/core/soong.mk b/core/soong.mk
index e070d6b..e3ce46e 100644
--- a/core/soong.mk
+++ b/core/soong.mk
@@ -16,10 +16,15 @@
 
 SOONG := $(SOONG_OUT_DIR)/soong
 SOONG_BUILD_NINJA := $(SOONG_OUT_DIR)/build.ninja
-SOONG_ANDROID_MK := $(SOONG_OUT_DIR)/Android.mk
 SOONG_VARIABLES := $(SOONG_OUT_DIR)/soong.variables
 SOONG_IN_MAKE := $(SOONG_OUT_DIR)/.soong.in_make
 
+# Only include the Soong-generated Android.mk if we're merging the
+# Soong-defined binaries with Kati-defined binaries.
+ifeq ($(USE_SOONG),true)
+SOONG_ANDROID_MK := $(SOONG_OUT_DIR)/Android.mk
+endif
+
 # Bootstrap soong.  Run only the first time for clean builds
 $(SOONG):
 	$(hide) mkdir -p $(dir $@)
@@ -67,6 +72,8 @@
 	$(hide) mkdir -p $(dir $@)
 	$(hide) touch $@
 
-# Build an Android.mk listing all soong outputs as prebuilts
-$(SOONG_ANDROID_MK): $(SOONG) $(SOONG_VARIABLES) $(SOONG_IN_MAKE) FORCE
+# Run Soong, this implicitly create an Android.mk listing all soong outputs as
+# prebuilts.
+.PHONY: run_soong
+run_soong: $(SOONG) $(SOONG_VARIABLES) $(SOONG_IN_MAKE) FORCE
 	$(hide) $(SOONG) $(SOONG_BUILD_NINJA) $(NINJA_ARGS)