fix some violations of warning undef in folly/lang/New.h

Summary:
Tweaks for the following violations of warning `undef`:

```
folly/lang/New.h:86:5: error: '__cpp_sized_deallocation' is not defined, evaluates to 0 [-Werror,-Wundef]
#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
    ^
folly/lang/New.h:86:45: error: '_CPPLIB_VER' is not defined, evaluates to 0 [-Werror,-Wundef]
#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
                                            ^
folly/lang/New.h:106:5: error: '__cpp_sized_deallocation' is not defined, evaluates to 0 [-Werror,-Wundef]
#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
    ^
folly/lang/New.h:106:45: error: '_CPPLIB_VER' is not defined, evaluates to 0 [-Werror,-Wundef]
#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
                                            ^
```

Reviewed By: Orvid

Differential Revision: D46914069

fbshipit-source-id: d80cdf3c295d9dd14674a3e67ed790290f1973b5

folly/lang/New.h

@@ -35,7 +35,23 @@ namespace folly {
 #define FOLLY_DETAIL_LANG_NEW_IMPL_D ::operator delete
 #endif
 
-#if __cpp_aligned_new >= 201606 || _CPPLIB_VER
+#if defined(__cpp_aligned_new) && __cpp_aligned_new >= 201606
+#define FOLLY_DETAIL_LANG_NEW_HAVE_AN 1
+#elif defined(_CPPLIB_VER)
+#define FOLLY_DETAIL_LANG_NEW_HAVE_AN 1
+#else
+#define FOLLY_DETAIL_LANG_NEW_HAVE_AN 0
+#endif
+
+#if defined(__cpp_sized_deallocation) && __cpp_sized_deallocation >= 201309L
+#define FOLLY_DETAIL_LANG_NEW_HAVE_SD 1
+#elif defined(_CPPLIB_VER) && !__clang__
+#define FOLLY_DETAIL_LANG_NEW_HAVE_SD 1
+#else
+#define FOLLY_DETAIL_LANG_NEW_HAVE_SD 0
+#endif
+
+#if FOLLY_DETAIL_LANG_NEW_HAVE_AN
 using std::align_val_t;
 #else
 enum class align_val_t : std::size_t {};
@@ -55,7 +71,7 @@ struct operator_new_fn {
   FOLLY_NODISCARD FOLLY_ERASE void* operator()( //
       std::size_t const s,
       FOLLY_MAYBE_UNUSED align_val_t const a) const {
-#if __cpp_aligned_new >= 201606 || _CPPLIB_VER
+#if FOLLY_DETAIL_LANG_NEW_HAVE_AN
     return FOLLY_DETAIL_LANG_NEW_IMPL_N(s, a);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_N(s);
@@ -65,7 +81,7 @@ struct operator_new_fn {
       std::size_t const s,
       FOLLY_MAYBE_UNUSED align_val_t const a,
       std::nothrow_t const&) const noexcept {
-#if __cpp_aligned_new >= 201606 || _CPPLIB_VER
+#if FOLLY_DETAIL_LANG_NEW_HAVE_AN
     return FOLLY_DETAIL_LANG_NEW_IMPL_N(s, a, std::nothrow);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_N(s, std::nothrow);
@@ -83,7 +99,7 @@ struct operator_delete_fn {
   FOLLY_ERASE void operator()( //
       void* const p,
       FOLLY_MAYBE_UNUSED std::size_t const s) const noexcept {
-#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
+#if FOLLY_DETAIL_LANG_NEW_HAVE_SD
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p, s);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p);
@@ -92,7 +108,7 @@ struct operator_delete_fn {
   FOLLY_ERASE void operator()( //
       void* const p,
       FOLLY_MAYBE_UNUSED align_val_t const a) const noexcept {
-#if __cpp_aligned_new >= 201606 || _CPPLIB_VER
+#if FOLLY_DETAIL_LANG_NEW_HAVE_AN
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p, a);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p);
@@ -102,14 +118,14 @@ struct operator_delete_fn {
       void* const p,
       FOLLY_MAYBE_UNUSED std::size_t const s,
       FOLLY_MAYBE_UNUSED align_val_t const a) const noexcept {
-#if __cpp_aligned_new >= 201606 || _CPPLIB_VER
-#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
+#if FOLLY_DETAIL_LANG_NEW_HAVE_AN
+#if FOLLY_DETAIL_LANG_NEW_HAVE_SD
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p, s, a);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p, a);
 #endif
 #else
-#if __cpp_sized_deallocation >= 201309L || (_CPPLIB_VER && !__clang__)
+#if FOLLY_DETAIL_LANG_NEW_HAVE_SD
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p, s);
 #else
     return FOLLY_DETAIL_LANG_NEW_IMPL_D(p);