Include target api version in build system for rscpp.

b/23161320

Change-Id: Ibc23309abed092e7648168fbf4b80891a44929a6
diff --git a/core/definitions.mk b/core/definitions.mk
index f20b2b7..35e3a79 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -903,6 +903,7 @@
   -d $(PRIVATE_RS_OUTPUT_DIR) \
   -a $@ -MD \
   -reflect-c++ \
+  $(addprefix -target-api , $(PRIVATE_RS_TARGET_API)) \
   $(PRIVATE_RS_FLAGS) \
   $(addprefix -I , $(PRIVATE_RS_INCLUDES)) \
   $(PRIVATE_RS_SOURCE_FILES)