Predefined macros defined for a custom compiler are not completed and highlighted

Toolchain Defines are not passed to the editor code model. Defines are correctly visible in C++ Code Model Inspector but the editor doesn't highlight nor code complete them.

 
Steps to reproduce:

1. Add custom C or C++ compiler from Options -> Kits -> Compilers tab
2. Add predefined macros for the compiler
3. Create a new kit or switch any older kit to use the custom compiler
4. Create a new project that uses the kit with the custom compiler
5. Try to use the predefined macro in any C or C++ source file

Expected result:

1. The predefined macro is correctly highlighted and code completed in the editor.

Actual result:

Issue occurs with both CMake and QMake projects.

I have only tested with 4.12.4, but probably affects more versions.  This feature worked earlier (at least some time last year) so this is regression.