Don't define StdAllocator<void> from C++17.

Author: ylavic

include/rapidjson/allocators.h

@@ -581,6 +581,7 @@ class StdAllocator :
     BaseAllocator baseAllocator_;
 };
 
+#if !RAPIDJSON_HAS_CXX17 // std::allocator<void> deprecated in C++17
 template <typename BaseAllocator>
 class StdAllocator<void, BaseAllocator> :
     public std::allocator<void>
@@ -628,6 +629,7 @@ class StdAllocator<void, BaseAllocator> :
 
     BaseAllocator baseAllocator_;
 };
+#endif
 
 #ifdef __GNUC__
 RAPIDJSON_DIAG_POP

test/unittest/allocatorstest.cpp

@@ -83,8 +83,12 @@ struct TestStdAllocatorData {
 
 template <typename Allocator>
 void TestStdAllocator(const Allocator& a) {
+#if RAPIDJSON_HAS_CXX17
+    typedef StdAllocator<bool, Allocator> BoolAllocator;
+#else
     typedef StdAllocator<void, Allocator> VoidAllocator;
     typedef typename VoidAllocator::template rebind<bool>::other BoolAllocator;
+#endif
     BoolAllocator ba(a), ba2(a);
     EXPECT_TRUE(ba == ba2);
     EXPECT_FALSE(ba!= ba2);