adding rb_warn gives a segmentation fault

I want to add some traces to rb_define_class and put a few rb_warn()  
calls in the class.c of a clean 1.8.5 source tree. With those extra  
lines make gives a segmentation fault:

gcc -g -O2 -pipe -fno-common  -DRUBY_EXPORT  -I. -I.  -c main.c
gcc main.o  libruby-static.a -ldl -lobjc   -o miniruby -g -O2 -pipe - 
fno-common  -DRUBY_EXPORT
/usr/bin/ld: warning multiple definitions of symbol _setregid
libruby-static.a(process.o) definition of _setregid in section  
(__TEXT,__text)
/usr/lib/gcc/i686-apple-darwin8/4.0.1/../../../libdl.dylib 
(setregid.So) definition of _setregid
/usr/bin/ld: warning multiple definitions of symbol _setreuid
libruby-static.a(process.o) definition of _setreuid in section  
(__TEXT,__text)
/usr/lib/gcc/i686-apple-darwin8/4.0.1/../../../libdl.dylib 
(setreuid.So) definition of _setreuid
make: *** [.rbconfig.time] Segmentation fault

I've been playing around removing some of them, moving them around,  
etc., to no avail, I get always that segmentation fault at the same  
point. Why?

-- fxn

VALUE
rb_define_class(name, super)
     const char *name;
     VALUE super;
{
     VALUE klass;
     ID id;

     rb_warn("defining %s", name);
     id = rb_intern(name);
     if (rb_const_defined(rb_cObject, id)) {
         rb_warn("reopening");
	klass = rb_const_get(rb_cObject, id);
	if (TYPE(klass) != T_CLASS) {
	    rb_raise(rb_eTypeError, "%s is not a class", name);
	}
	if (rb_class_real(RCLASS(klass)->super) != super) {
	    rb_name_error(id, "%s is already defined", name);
	}
	return klass;
     }
     if (!super) {
	rb_warn("no super class for `%s', Object assumed", name);
     }
     rb_warn("not seen before");
     klass = rb_define_class_id(id, super);
     st_add_direct(rb_class_tbl, id, klass);
     rb_name_class(klass, id);
     rb_const_set(rb_cObject, id, klass);
     rb_class_inherited(super, klass);

     return klass;
}