Fix deduction guide macro guard for Replaceable (#1097)

Summary:
- `Replaceable` defines a deduction guide if the feature test macro for
  it is met, or if we are on MSVC. However, the MSVC version that folly
  supports also defines the feature test macro for deduction guides. As
  such, remove the extra check for MSVC.
- Add `ReplaceableTest` to the  cmake build.
- Add test for deduction guide.
Pull Request resolved: https://github.com/facebook/folly/pull/1097

Reviewed By: Orvid

Differential Revision: D14699047

Pulled By: yfeldblum

fbshipit-source-id: ee62bae0f4b05f1a110c2bd90470fecbb0666d24

folly/Replaceable.h

@@ -637,7 +637,7 @@ class alignas(T) Replaceable
   aligned_storage_for_t<T> storage_[1];
 };
 
-#if __cpp_deduction_guides >= 201703 || _MSC_VER
+#if __cpp_deduction_guides >= 201703
 template <class T>
 Replaceable(T)->Replaceable<T>;
 #endif

folly/test/ReplaceableTest.cpp

@@ -334,3 +334,11 @@ TEST(ReplaceableTest, swapMemberFunctionDelegatesToUserSwap) {
   r1.swap(r2);
   EXPECT_TRUE(r1->calledSwap);
 }
+
+#if __cpp_deduction_guides >= 201703
+TEST(ReplaceableTest, DeductionGuide) {
+  Basic b{};
+  Replaceable r{b};
+  EXPECT_TRUE((std::is_same_v<Replaceable<Basic>, decltype(r)>));
+}
+#endif