Fix compilation of folly/Bits.h with MSVC

Summary:
This diff fixes compilation of folly/Bits.h with MSVC by checking for both <bit>/C++ version and checking for the __cpp_lib flag for std::bit_set. When compiling F14Table.cpp with MSVC and C++20, the <bit> check was passing while the check for __cpp_lib_bit_cast was failing.

This also corrects two uses of bit_cast to use folly::bit_cast.

Reviewed By: Gownta

Differential Revision: D49357730

fbshipit-source-id: c741a7b9f4b1862af6c0110a52d720337ff58748

folly/hash/Hash.h

@@ -749,7 +749,7 @@ struct hasher<T*> {
   using folly_is_avalanching = hasher<std::uintptr_t>::folly_is_avalanching;
 
   size_t operator()(T* key) const {
-    return Hash()(bit_cast<std::uintptr_t>(key));
+    return Hash()(folly::bit_cast<std::uintptr_t>(key));
   }
 };
 

folly/lang/Bits.h

@@ -67,13 +67,13 @@
 #include <folly/lang/Assume.h>
 #include <folly/portability/Builtins.h>
 
-#if __has_include(<bit>) && __cplusplus >= 202002L
+#if __has_include(<bit>) && (__cplusplus >= 202002L || (defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L))
 #include <bit>
 #endif
 
 namespace folly {
 
-#ifdef __cpp_lib_bit_cast
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
 
 using std::bit_cast;
 

folly/synchronization/DistributedMutex-inl.h

@@ -1380,7 +1380,8 @@ FOLLY_ALWAYS_INLINE std::uintptr_t tryWake(
     // we need release here because of the write to waker_ and also because we
     // are unlocking the mutex, the thread we do the handoff to here should
     // see the modified data
-    new (&waiter->metadata_) Metadata{waker, bit_cast<uintptr_t>(sleepers)};
+    new (&waiter->metadata_)
+        Metadata{waker, folly::bit_cast<uintptr_t>(sleepers)};
     waiter->futex_.store(kWake, std::memory_order_release);
     return 0;
   }