os x从10.10更新到10.11后，原有代码编译报错，#include <openssl/ssl.h>等头文件无法找到: "openssl/ssl.h: No such file or directory".
原有环境：os x10.10+Xcode6
更新后的环境：os x10.11+Xcode7, Qt5.3.1+Qt Creator 3.3.0
解决办法：
1.命令行执行：xcode-select —install,安装xcode命令行工具，/usr路径下出现include目录 (如果原来/usr/include目录已经存在，跳过这一步)；
/usr/include/openssl目录里包含了相关的头文件
2.在/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/路径下创建openssl目录；
3.把 /usr/include/openssl路径下的所有文件拷贝到刚建立的openssl目录下；
原因：
os x10.11开始，苹果sdk中不再提供openssl，在Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include路径下是找不到原有的openssl目录的。
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Sadly, it looks like we're not supposed to use it any more. As you say, it's included in the 10.10 SDK, but is deliberately missing from the 10.11 SDK.
http://lists.apple.com/archives/macnetworkprog/2015/Jun/msg00025.html
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参考：
1.https://forums.developer.apple.com/thread/3897
2.http://stackoverflow.com/questions/14655154/mac-os-x-lion-does-not-have-usr-include-folder
另外升级后，Qt Creator中编译会报找不到<sys/time.h>等系统头文件，修改~/Qt5.3.1/5.3/clang_64/mkspecs/qdevice.pri文件，把macsox10.10改为macosx10.11即可以解决问题。