Fix WCHAR_MAX, WCHAR_MIN, WINT_MAX, and WINT_MIN.

GCC tells us everything we need to know. clang does its usual half-assed job.

Change-Id: Id4d664529b10345274602768cd564d3df717e931

tests/wchar_test.cpp

@@ -155,3 +155,7 @@ TEST(wchar, wcstombs_wcrtombs) {
   bytes[3] = 0;
   EXPECT_STREQ("hix", bytes);
 }
+
+TEST(wchar, limits) {
+  ASSERT_LT(WCHAR_MIN, WCHAR_MAX);
+}