If the user who is compiling Cuik already has vcvars set, vcvars won't need to be initialized again. Helps with extra error message like "vcvars not found" in case of Visual Studio Developer Prompt that doesn't keep vcvars in it's PATH by default.
If vcvars weren't found in PATH a nice error message is displayed telling the user to either add it to PATH or use the Visual Studio Develeoper Command Prompt.
/Z7 doesn't emit an extra pdb (that's not essential for normal debugging) also fuck visual studio
Fixed a case of UB on calling strcmp with NULL argument that would trigger a crash on Windows if the argument to an option is not specified.
Changes: