Allow disabling turbine

m -j TURBINE_ENABLED=false will build without turbine.  This is
primarily useful for A/B comparisions of turbine builds, but will
also be used to temporarily disable turbine for unbundled builds
until we have turbine prebuilts.

Bug: 64308460
Test: m -j TURBINE_ENABLED=false java
Test: m -j java
Change-Id: Ie48746c8bfc60c361be9634cb1805ca1c09aa1fe
diff --git a/core/prebuilt_internal.mk b/core/prebuilt_internal.mk
index 24816e9..f1ea70e 100644
--- a/core/prebuilt_internal.mk
+++ b/core/prebuilt_internal.mk
@@ -468,8 +468,10 @@
 $(common_classes_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)
 
+ifneq ($(TURBINE_ENABLED),false)
 $(common_header_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)
+endif
 
 else # !LOCAL_IS_HOST_MODULE
 # for target java libraries, the LOCAL_BUILT_MODULE is in a product-specific dir,
@@ -520,8 +522,10 @@
 $(common_classes_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)
 
+ifneq ($(TURBINE_ENABLED),false)
 $(common_header_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)
+endif
 
 $(common_classes_pre_proguard_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)