How to set compiler flag (-fpermissive) in eclipse?

Hello everybody, I have a beginner question:

I would like to mix signed and unsigned char types.
Therefore I would like to know how to set the fpermissive flag.
I have tried different approaches, none of them give the result i would like to have:

-> properties of .cpp file, go to paths and symbols, #symbols, select GNU C++, add fpermissive value (none or value 1)

-> properties of project entire project: do the same

-> properties of .bsp: do the same.

-> properties of C/C++ build, build variables, fpermissive, value 1

The strange thing is that if i go through a find in files (simple and tried out find in files with microsoft visual studio), i do see that the settings have been added to the .cproject but are not in the makefile. It is possible that it is passed through the ALT_CPPFLAGS_DEFINED system variabele, but the detailed mechanism behind, i do not know.

I aslo do not know what steps to take to activate the changed settings, is a clean and rebuild of the project ok, or are there other steps to be taken?

Would anybody please be so kind to explain in detail how i can set the fpermissive flag (and others)?

Best Regards,
John.