ldd: reference readelf instead of objdump in warning message

We have an obsolete GNU objdump 2.17.50 in the base system, which will
be removed in the future.  Suggest readelf(1) for examining ELF files
instead; for most use cases it is the preferred tool anyhow.

PR:		229046
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation

usr.bin/ldd/sods.c

@@ -203,7 +203,7 @@ dump_file(const char *fname)
     file_base = (const char *) objbase;	/* Makes address arithmetic easier */
 
     if (IS_ELF(*(const Elf32_Ehdr*) align_struct(file_base))) {
-	warnx("%s: this is an ELF program; use objdump to examine", fname);
+	warnx("%s: this is an ELF program; use readelf to examine", fname);
 	++error_count;
 	munmap(objbase, sb.st_size);
 	return;