Eliminate filename length restrictions, remote ofmt->filename()

Get rid of remaining dependencies on FILENAME_MAX, which ought to have
been removed a long time ago.

Remove ofmt->filename(); all implementations pretty much do the same
thing and there is absolutely no reason to duplicate that
functionality all over the place.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

include/compiler.h

@@ -155,6 +155,10 @@ int vsnprintf(char *, size_t, const char *, va_list);
 size_t strlcpy(char *, const char *, size_t);
 #endif
 
+#if !defined(HAVE_STRCHRNUL) || !HAVE_DECL_STRCHRNUL
+char *strrchrnul(const char *, int);
+#endif
+
 #ifndef __cplusplus		/* C++ has false, true, bool as keywords */
 # ifdef HAVE_STDBOOL_H
 #  include <stdbool.h>