新装的VS2015，调试旧的代码报错，信息如下：
MSB8020 The build tools for v120 (Platform Toolset = 'v120') cannot be found. To build using the v120 build tools, please install v120 build tools. Alternatively, you may upgrade to the current Visual Studio tools by selecting the Project menu or right-click
the solution, and then selecting "Retarget solution". Gtk-sfr-Demo C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.Cpp.Platform.targets 57
看到错误，首先想到可能是因为之前的工程是用VS2013开发的，需要设置。 果断百度之……
平台工具集 改为VS2015支持的即可： Visual Studio 2015 (v140)