When you build a project or solution in Visual Studio, the entire command line used to run the compiler (csc.exe, including switches and parameters) is displayed in the Output window. If you don’t see it there, check the Verbosity level by going to:
Options > Projects and Solutions > Build and Run > MSBuild project build output verbosity
(You may need to choose “Show all settings”)
It has to be set to “Normal” or higher. Check this question and answer for more details:
To see all command line on output window while compiling