Need to turn warnings for unkown attribute into error in TI-ARM-Clang

Hello,
as I am currently wrting a program that finds out for different compilers what "__attribute__" specifiers are supported,
and therefore I let CMake try to compile some example code for every attribute specifier, I need a way to tell the compiler
that unkown-attribute-warnings shall be treated as error.

So I followed this guide:

clang.llvm.org/.../UsersManual.html


together with:

https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-attributes



but when I run the Script I get in CMakeFiles/CMakeError.log the following:



Telling me that there is no Warning "unknown-attributes".

What would I have to use instead in TI-ARM-Clang to make encountering unknown attributes an error ?
Thank you for your help.


Best regards

Philip.