Pass USE_SAFESTACK to Soong.

Change-Id: I51a94da0942aa1a1e003c134a30e8da82e1270b8
diff --git a/core/soong.mk b/core/soong.mk
index f1d765c..ebcccd3 100644
--- a/core/soong.mk
+++ b/core/soong.mk
@@ -65,7 +65,8 @@
 	echo ''; \
 	echo '    "CrossHost": "$(HOST_CROSS_OS)",'; \
 	echo '    "CrossHostArch": "$(HOST_CROSS_ARCH)",'; \
-	echo '    "CrossHostSecondaryArch": "$(HOST_CROSS_2ND_ARCH)"'; \
+	echo '    "CrossHostSecondaryArch": "$(HOST_CROSS_2ND_ARCH)",'; \
+	echo '    "Safestack": $(if $(filter true,$(USE_SAFESTACK)),true,false)'; \
 	echo '}') > $(SOONG_VARIABLES_TMP); \
 	if ! cmp -s $(SOONG_VARIABLES_TMP) $(SOONG_VARIABLES); then \
 	  mv $(SOONG_VARIABLES_TMP) $(SOONG_VARIABLES); \