fixed error to get the value of VCTargetsPath:

Error:

E:\work\git\third\grpc\grpc\.build>cmake .. -G "Visual Studio 14 2015" -DCMAKE_BUILD_TYPE=Release
CMake Error at CMakeLists.txt:31 (project):
  Failed to run MSBuild command:
    MSBuild.exe
  to get the value of VCTargetsPath:
    system can not find the file specified.

How fixed it:

open "Developer Command Prompt for VS 2017" in start menu. or it's content is:

%comspec% /k "D:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Tools\VsDevCmd.bat"

Last:
 can run now.