Fix -version information for llvm-rs-cc.

Change-Id: I30caa96c139308c71d912f19df2119e31025ffe3
diff --git a/Android.mk b/Android.mk
index 5b2b7eb..fce3637 100644
--- a/Android.mk
+++ b/Android.mk
@@ -23,6 +23,7 @@
 ifneq ($(TARGET_BUILD_VARIANT),eng)
 local_cflags_for_slang += -D__DISABLE_ASSERTS
 endif
+local_cflags_for_slang += -DTARGET_BUILD_VARIANT=$(TARGET_BUILD_VARIANT)
 
 ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"
   RS_VERSION := $(PLATFORM_SDK_VERSION)