configurator: Return pointer difference as ptrdiff_t

On LLP64 systems (like 64-bit Windows) long is 32 bits while pointers
are 64 bits, which results in a warning similar to the following:

warning C4244: 'return': conversion from '__int64' to 'long', possible loss of data

for HAVE_STACK_GROWS_UPWARDS.  Fix this by using the ptrdiff_t type
introduced by C99 for this purpose.
Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tools/configurator/configurator.c

@@ -278,7 +278,8 @@ static struct test tests[] = {
 	  "	return __stop_mysec - __start_mysec;\n"
 	  "}\n" },
 	{ "HAVE_STACK_GROWS_UPWARDS", DEFINES_EVERYTHING|EXECUTE, NULL, NULL,
-	  "static long nest(const void *base, unsigned int i)\n"
+	  "#include <stddef.h>\n"
+	  "static ptrdiff_t nest(const void *base, unsigned int i)\n"
 	  "{\n"
 	  "	if (i == 0)\n"
 	  "		return (const char *)&i - (const char *)base;\n"