Why would you do that?
Because it will be easier in the longer period of time. You won't have to worry if the options is C or C++.
Another benefit is that this will bring us one step closer to multy-language/multi-compiler support in a single project.
MSVC for example is one compiler for all.
In fact MSVC is MSVC++, I doubt there is any support for C provided by Microsoft, and if I remember correctly, they stated that C11 won't be supported by them.
Edit: I'm talking about the options added in "compiler->other options", because you can't add "-Werror=return-type" in the normal options. So thinking about this again, splitting the compilers in C and C++ ones is the only available option.