sh: Don't modify exit status when break/continue/return passes !.

This matches what would happen if  ! P  were to be replaced with
if P; then false; else true; fi.

Example:
  f() { ! return 0; }; f

bin/sh/eval.c

@@ -279,6 +279,8 @@ evaltree(union node *n, int flags)
 			break;
 		case NNOT:
 			evaltree(n->nnot.com, EV_TESTED);
+			if (evalskip)
+				goto out;
 			exitstatus = !exitstatus;
 			break;
 

tools/regression/bin/sh/execution/not1.0

@@ -0,0 +1,4 @@
+# $FreeBSD$
+
+f() { ! return $1; }
+f 0 && ! f 1

tools/regression/bin/sh/execution/not2.0

@@ -0,0 +1,6 @@
+# $FreeBSD$
+
+while :; do
+	! break
+	exit 3
+done