Compiling with last NDK + some hardening

Patch received in https://github.com/matrix-org/olm/issues/13

android/olm-sdk/src/main/jni/Android.mk

@@ -21,6 +21,9 @@ LOCAL_CFLAGS+= -DOLMLIB_VERSION_MAJOR=$(MAJOR) \
 
 #LOCAL_CFLAGS+= -DNDK_DEBUG
 
+LOCAL_CFLAGS+=-fstack-protector-all -D_FORTIFY_SOURCE=2 -Wformat -Wformat-security -Wall
+LOCAL_LDFLAGS=-z relro -z now
+
 LOCAL_C_INCLUDES+= $(LOCAL_PATH)/$(SRC_ROOT_DIR)/include/ \
 $(LOCAL_PATH)/$(SRC_ROOT_DIR)/lib
 

android/olm-sdk/src/main/jni/Application.mk

 APP_PLATFORM := android-16
-APP_ABI := arm64-v8a armeabi-v7a armeabi x86_64  x86
-APP_STL := gnustl_static
\ No newline at end of file
+APP_ABI := arm64-v8a armeabi-v7a x86_64 x86
+APP_STL := gnustl_static

android/olm-sdk/src/main/jni/olm_jni.h

@@ -21,6 +21,7 @@
 #include <cstdlib>
 #include <cstdio>
 #include <string>
+#include <string.h>
 #include <sstream>
 #include <jni.h>
 #include <android/log.h>