Update build to properly use prebuilt llvm-rs-cc.

Change-Id: I52a83066b6c08d05d69db4f93631eeaf9c0b41c6
diff --git a/core/definitions.mk b/core/definitions.mk
index 4c499ad..466a482 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -801,6 +801,7 @@
   -p $(PRIVATE_RS_OUTPUT_DIR)/src \
   -d $(PRIVATE_RS_OUTPUT_DIR) \
   -a $@ -MD \
+  $(addprefix -target-api , $(PRIVATE_RS_TARGET_API)) \
   $(foreach inc,$(PRIVATE_RS_INCLUDES),$(addprefix -I , $(inc))) \
   $(PRIVATE_RS_SOURCE_FILES)
 #$(hide) $(LLVM_RS_LINK) \