Disallow rtti

I am currently starting implementing a new toolchain and want to disable rtti there.
Now saw CalculateRTTIMode in lib/Driver/ToolChain.cpp. Now I would like to warn the user that rtti is actually no supported on that platform (for -frtti). Currently it seems like all rtti handling in Toolchain is hard coded.
What is the best way to indicate missing rtti on a platform?

How is it "missing"? You just want to have a policy that those language features don't work on your target? We don't have any existing targets that do that, so it's not surprising that you might need to provide some customization hook for it.

John.

Darn - email lost the 'cfe-dev'

With only 128KB of ROM, you’re going to find it hard to fit a C++ runtime library (though if you rip out the demangler you’ll save quite a lot), so even if you compile with RTTI, you won’t be able to use it or throw exceptions. A stack unwinder plus the C++ personality function can easily add up to more than the ROM on such devices. It’s possible to fit just enough support for dynamic_cast on such a system, but it’s somewhat awkward to have dynamic_cast working but exceptions not working.

David

Exactly that.
So will have no RTTI, no dynamic_cast, no thread_local, no exceptions, no new, no libc++
Just a very stripped down version of C++ (is there any other similar, stripped down toolchain!?).
Still trying to find, how I can have the code fail when attempting rtti. Seems like there is no such capability via the Driver interface.