kstrto*: accept "-0" for signed conversion

strtol(3) et al accept "-0", so should we.

Signed-off-by: Alexey Dobriyan <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Joel Becker <[e-mail]>
Cc: Mark Fasheh <[e-mail]>
Cc: Theodore Ts'o <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/kstrtox.c

···
 		rv = _kstrtoull(s + 1, base, &tmp);
 		if (rv < 0)
 			return rv;
-		if ((long long)(-tmp) >= 0)
+		if ((long long)-tmp > 0)
 			return -ERANGE;
 		*res = -tmp;
 	} else {

lib/test-kstrtox.c

···
 		{"4294967297",	10,	4294967297LL},
 		{"9223372036854775807",	10,	9223372036854775807LL},
 
+		{"-0",	10,	0LL},
 		{"-1",	10,	-1LL},
 		{"-2",	10,	-2LL},
 		{"-9223372036854775808",	10,	LLONG_MIN},
···
 		{"-9223372036854775809",	10},
 		{"-18446744073709551614",	10},
 		{"-18446744073709551615",	10},
-		/* negative zero isn't an integer in Linux */
-		{"-0",	0},
-		{"-0",	8},
-		{"-0",	10},
-		{"-0",	16},
 		/* sign is first character if any */
 		{"-+1", 0},
 		{"-+1", 8},