constant: skip E2BIG test on GNU/Hurd

Hurd doesn't use 7 for E2BIG, so this string test would fail if the
test itself were more precise.

Author: jmdh

dist/constant/t/constant.t

@@ -92,11 +92,14 @@ is ZERO3, '0.0';
 cmp_ok(abs(PI - 3.1416), '<', 0.0001);
 is Other::PI, 3.141;
 
-use constant E2BIG => $! = 7;
-cmp_ok E2BIG, '==', 7;
-# This is something like "Arg list too long", but the actual message
-# text may vary, so we can't test much better than this.
-cmp_ok length(E2BIG), '>', 6;
+SKIP: {
+    skip "GNU/Hurd doesn't use 7 as E2BIG", 2 if $^O eq "gnu";
+    use constant E2BIG => $! = 7;
+    cmp_ok E2BIG, '==', 7;
+    # This is something like "Arg list too long", but the actual message
+    # text may vary, so we can't test much better than this.
+    cmp_ok length(E2BIG), '>', 6;
+}
 
 is @warnings, 0 or diag join "\n- ", "unexpected warning:", @warnings;
 @warnings = ();		# just in case