原因：没有加入支持的共享库
出错时：
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := testlog
LOCAL_SRC_FILES := testlog.c
include $(BUILD_SHARED_LIBRARY)
.c的头文件
#include <string.h>
#include <jni.h>
#include <android/log.h>
调试好的：
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := testlog
LOCAL_SRC_FILES := testlog.c
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)
.c的头文件
#include <string.h>
#include <jni.h>
#include <android/log.h>