teemperor@ftldrive ~/c/p/test> ls
CPP.cf
teemperor@ftldrive ~/c/p/test> bnfc -m -cpp CPP.cf 
65 rules accepted
writing new file ./Absyn.H
writing new file ./Absyn.C
writing new file ./CPP.l
writing new file ./CPP.y
writing new file ./Parser.H
writing new file ./Skeleton.H
writing new file ./Skeleton.C
writing new file ./Printer.H
writing new file ./Printer.C
writing new file ./Test.C
writing new file ./Makefile
teemperor@ftldrive ~/c/p/test> make CC=clang++
[lots of warnings]
CPP.l:76:68: warning: control reaches end of non-void function [-Wreturn-type]
int initialize_lexer(FILE *inp) { yyrestart(inp); BEGIN YYINITIAL; }
46 warnings generated.
clang++ -g -W -Wall -c Test.C
Linking TestCPP...
clang++ -g -W -Wall Absyn.o Lexer.o Parser.o Printer.o Test.o -o TestCPP
teemperor@ftldrive ~/c/p/test> ./TestCPP < /dev/null 
fish: “./TestCPP < /dev/null” terminated by signal SIGILL (Illegal instruction)

> grep -R initialize_lexer
CPP.l:void initialize_lexer(FILE *inp) { yyrestart(inp); BEGIN YYINITIAL; }
CPP.y:int initialize_lexer(FILE * inp);