grep: turn off -w if -x is specified

-x overcomes -w in gnugrep, and it should here as well.  Flip it off as
needed to avoid confusing other parts of grep.

usr.bin/grep/grep.1

@@ -30,7 +30,7 @@
 .\"
 .\"	@(#)grep.1	8.3 (Berkeley) 4/18/94
 .\"
-.Dd November 19, 2020
+.Dd February 4, 2021
 .Dt GREP 1
 .Os
 .Sh NAME
@@ -405,6 +405,9 @@ and
 .Sq [[:>:]] ;
 see
 .Xr re_format 7 ) .
+This option has no effect if
+.Fl x
+is also specified.
 .It Fl x , Fl Fl line-regexp
 Only input lines selected against an entire fixed string or regular
 expression are considered to be matching lines.

usr.bin/grep/grep.c

@@ -630,6 +630,10 @@ main(int argc, char *argv[])
 	aargc -= optind;
 	aargv += optind;
 
+	/* xflag takes precedence, don't confuse the matching bits. */
+	if (wflag && xflag)
+		wflag = false;
+
 	/* Fail if we don't have any pattern */
 	if (aargc == 0 && needpattern)
 		usage();