It's __func__. You can find it in assert.h and in the help file under "What is ISO C99?." __func__ needs to be added to "Predefined preprocessor symbols (POCC)".
The "Predefined preprocessor symbols (POCC)" are much too hard to find in the Pelles help. I know they are there yet it takes me a few minutes slogging through the help to figure out what page points to them. There should be an index entry called "Predefined preprocessor symbols (POCC)" and "Predefined preprocessor symbols (POCC)" should be referenced directly from #ifdef, #define, #undef, "C preprocessor defined operator", "C preprocessor stringizing operator (#)", and "/D option (POCC)"
Other index topics are necessary
"define" -> #define
"defined" -> "C preprocessor defined operator"
"predefined" -> "Predefined preprocessor symbols (POCC)"
"macros" -> "C preprocessor macros"
"preprocessor" -> "C preprocessor"
"Command line options" -> "Command line options (POCC)", "Command line options (PODUMP)", ...
I should be able to type any preprocessor keyword that comes to mind and be no more than 2 clicks from "Predefined preprocessor symbols (POCC)".