Error CS2006 - Missing argument for '/define:' option

As the title says, getting a strange error where nearly all scripts aside from Unity’s own have stopped loading in the editor. This is the lone error that comes up in the console. Debugging in Visual Studio shows the following error in both the project and project.editor:

Missing '<text>' for '-define:' option

I have absolutely no idea what changed to cause the error. I’m using Unity 5.6.1f1 and Visual Studio 2017 Community. For what its worth i’m also using the HoloToolkit asset for Hololens development.

Any help or pointers in the right direction would be hugely appreciated, tried googling but no one else seems to have had this problem.

After installed Unity2018.3.8, when I open a project created with Unity2017.3.1, I see similar error:

error CS2006: Missing argument for /define:' option error CS2006: Missing argument for /define:’ option

How to fix it?,After installing Unity 2018.3.8f1, when I open an project created with Unity 2017.3.1f1, a similar error display in the console window:

error CS2006: Missing argument for /define:' option error CS2006: Missing argument for /define:’ option

In my case, finally I found warning that mcs.rsp is obsolete. So I changed mcs.rsp to csc.rsp as recommended and restarted Unity to let the compiler work. Then everything goes right.
I guess mcs.rsp is nolonger supported by new compiler so it throws an error but Unity failed to tell us which file goes wrong. So check some pre-processing file.
I hope this will be of some help:),In my case, finally I found “mcs.rsp” in project got a warning that it’s obsolete. I changed name to csc.rsp as recommanded and restarted Unity. Everything turned to be alright.
Maybe mcs.rsp is no longer supported by new C# compiler so it throws error but unity console failed to tell us which file goes wrong.
Hope this will be of some help.