Replace setproctitle dummy macro with a function stub

This way we can replace it later on with a real implementation so that
applications can immediately benefit from it w/o the need to recompile
them.

include/bsd/unistd.h

@@ -37,6 +37,8 @@
 __BEGIN_DECLS
 mode_t getmode(const void *set, mode_t mode);
 void *setmode(const char *mode_str);
+
+void setproctitle(const char *fmt, ...);
 __END_DECLS
 
 #endif