Enable goma in soong

Pass the USE_GOMA flag to soong, and export the CC_WRAPPER environment
variable after adding gomacc to it.

Bug: 31142427
Change-Id: I6de698a40817c0615b03fa17bd27075465d79ffd
diff --git a/core/ninja.mk b/core/ninja.mk
index 533553e..04efcc1 100644
--- a/core/ninja.mk
+++ b/core/ninja.mk
@@ -131,8 +131,8 @@
 
 $(COMBINED_BUILD_NINJA): $(KATI_BUILD_NINJA)
 	$(hide) echo "builddir = $(OUT_DIR)" > $(COMBINED_BUILD_NINJA)
-	$(hide) echo "subninja $(SOONG_BUILD_NINJA)" >> $(COMBINED_BUILD_NINJA)
-	$(hide) echo "subninja $(KATI_BUILD_NINJA)" >> $(COMBINED_BUILD_NINJA)
+	$(hide) echo "include $(KATI_BUILD_NINJA)" >> $(COMBINED_BUILD_NINJA)
+	$(hide) echo "include $(SOONG_BUILD_NINJA)" >> $(COMBINED_BUILD_NINJA)
 
 $(sort $(DEFAULT_GOAL) $(ANDROID_GOALS)) : ninja_wrapper
 	@#empty