Provide defined value for $TODO only where test should not run.

Some tests should not be run on older perls.  To indicate that, provide
an undef rather than a defined but false value.

This reflects Test::Builder synch with CPAN for upstream bug fix:
Test-More/test-more@9c269ff

Note that these should really be SKIPs rather than TODOs (but we can handle that later).

ext/Devel-Peek/t/Peek.t

@@ -286,8 +286,7 @@ do_test('reference to hash',
     MAX = 7
     Elt "123" HASH = $ADDR' . $c_pattern,
 	'',
-	$] < 5.015
-	 && 'The hash iterator used in dump.c sets the OOK flag');
+	($] < 5.015) ? 'The hash iterator used in dump.c sets the OOK flag' : undef);
 
 do_test('reference to anon sub with empty prototype',
         sub(){@_},
@@ -457,7 +456,7 @@ do_test('reference to blessed hash',
     FILL = 0
     MAX = 7', '',
 	$] >= 5.015
-	     ? 0
+	     ? undef
 	     : 'The hash iterator used in dump.c sets the OOK flag');
 
 do_test('typeglob',
@@ -535,7 +534,7 @@ do_test('reference to hash containing Unicode',
       COW_REFCNT = 1				# $] < 5.019007
 ',      '',
 	$] >= 5.015
-	    ?  0
+	    ? undef
 	    : 'The hash iterator used in dump.c sets the OOK flag');
 } else {
 do_test('reference to hash containing Unicode',
@@ -562,7 +561,7 @@ do_test('reference to hash containing Unicode',
       COW_REFCNT = 1				# $] < 5.019007
 ',      '',
 	$] >= 5.015
-	    ?  0
+	    ? undef
 	    : 'The hash iterator used in dump.c sets the OOK flag');
 }
 
@@ -767,7 +766,7 @@ do_test('blessing to a class with embedded NUL characters',
     FILL = 0
     MAX = 7', '',
 	$] >= 5.015
-	    ?  0
+	    ? undef
 	    : 'The hash iterator used in dump.c sets the OOK flag');
 
 do_test('ENAME on a stash',
@@ -928,7 +927,7 @@ do_test('small hash after keys and scalar',
 
 # Dump with arrays, hashes, and operator return values
 @array = 1..3;
-do_test('Dump @array', '@array', <<'ARRAY', '', '', 1);
+do_test('Dump @array', '@array', <<'ARRAY', '', undef, 1);
 SV = PVAV\($ADDR\) at $ADDR
   REFCNT = 1
   FLAGS = \(\)
@@ -953,7 +952,7 @@ SV = PVAV\($ADDR\) at $ADDR
     IV = 3
 ARRAY
 
-do_test('Dump @array,1', '@array,1', <<'ARRAY', '', '', 1);
+do_test('Dump @array,1', '@array,1', <<'ARRAY', '', undef, 1);
 SV = PVAV\($ADDR\) at $ADDR
   REFCNT = 1
   FLAGS = \(\)
@@ -969,7 +968,7 @@ SV = PVAV\($ADDR\) at $ADDR
 ARRAY
 
 %hash = 1..2;
-do_test('Dump %hash', '%hash', <<'HASH', '', '', 1);
+do_test('Dump %hash', '%hash', <<'HASH', '', undef, 1);
 SV = PVHV\($ADDR\) at $ADDR
   REFCNT = 1
   FLAGS = \(SHAREKEYS\)
@@ -986,7 +985,7 @@ SV = PVHV\($ADDR\) at $ADDR
 HASH
 
 $_ = "hello";
-do_test('rvalue substr', 'substr $_, 1, 2', <<'SUBSTR', '', '', 1);
+do_test('rvalue substr', 'substr $_, 1, 2', <<'SUBSTR', '', undef, 1);
 SV = PV\($ADDR\) at $ADDR
   REFCNT = 1
   FLAGS = \(PADTMP,POK,pPOK\)