[Qt-creator] Where can I find a list of Creator's variables?

[Nikos Chantziaras]

I have the issue of Creator using clang++ to build C++ sources, and GCC 
to build C sources. I am trying to fix this, but for the life of me I 
can't find a reference of Creator's variables anywhere.

In the kit that uses Clang, Creator uses this in the "CMake 
Configuration" field:

   CMAKE_CXX_COMPILER:STRING=%{Compiler:Executable}

That's nice. But CMAKE_C_COMPILER is not set, so I get a mixed Clang/GCC 
build. %{Compiler:Executable} is obviously the C++ compiler. What is the 
C compiler? What do I write here:

   CMAKE_C_COMPILER:STRING=%{???}