ar: enable deterministic mode by default

Ar cannot handle UIDs with more than 6 digits, and storing the mtime,
uid, gid and mode provides little to negative value anyhow for ar's
uses. Turn on deterministic (-D) mode by default; it can be disabled by
the user with -U.

PR:		196929
Relnotes:	Yes
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D3190

usr.bin/ar/ar.1

@@ -210,6 +210,7 @@ and 0644 instead of file mode from the members named by arguments
 .Ar .
 This ensures that checksums on the resulting archives are reproducible
 when member contents are identical.
+This option is enabled by default.
 If multiple
 .Fl D
 and

usr.bin/ar/ar.c

@@ -104,6 +104,8 @@ main(int argc, char **argv)
 
 	bsdar = &bsdar_storage;
 	memset(bsdar, 0, sizeof(*bsdar));
+	/* Enable deterministic mode by default. */
+	bsdar->options |= AR_D;
 
 	if ((bsdar->progname = getprogname()) == NULL)
 		bsdar->progname = "ar";