Implement P0599: 'noexcept for hash functions'. Fix a couple of hash functions (optional<T> and unique_ptr<T>) which were mistakenly marked as 'noexcept'. Reviewed as https://reviews.llvm.org/D31234

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@298573 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/unord.hash/floating.pass.cpp

@@ -24,6 +24,8 @@
 #include <limits>
 #include <cmath>
 
+#include "test_macros.h"
+
 template <class T>
 void
 test()
@@ -31,6 +33,7 @@ test()
     typedef std::hash<T> H;
     static_assert((std::is_same<typename H::argument_type, T>::value), "" );
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "" );
+    ASSERT_NOEXCEPT(H()(T()));
     H h;
 
     std::size_t t0 = h(0.);