Export OVERRIDE_RS_DRIVER to soong

Test: examine RS cflags
Change-Id: I0c1cc54f3f7f860895322d2825c7168c93a84ef5
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 9cda3b1..0a2208b 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -79,6 +79,7 @@
 	echo '    "Safestack": $(if $(filter true,$(USE_SAFESTACK)),true,false),'; \
 	echo '    "EnableCFI": $(if $(filter false,$(ENABLE_CFI)),false,true),'; \
 	echo '    "Device_uses_hwc2": $(if $(filter true,$(TARGET_USES_HWC2)),true,false),'; \
+	echo '    "Override_rs_driver": "$(OVERRIDE_RS_DRIVER)",'; \
 	echo ''; \
 	echo '    "ArtUseReadBarrier": $(if $(filter false,$(PRODUCT_ART_USE_READ_BARRIER)),false,true),'; \
 	echo ''; \