[libcxx] [test] In unord.hash/floating.pass.cpp, add a static_cast to fix a truncation warning.

[STL_MSFT]

Summary

In unord.hash/floating.pass.cpp, add a static_cast to fix a truncation warning.

Fixes MSVC warning C4305 "'argument': truncation from 'double' to 'const std::hash<float>::_Kty'".

[EricWF]

r272621.

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

 {
     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), "" );
     H h;
 
     std::size_t t0 = h(0.);
     std::size_t tn0 = h(-0.);
-    std::size_t tp1 = h(0.1);
+    std::size_t tp1 = h(static_cast<T>(0.1));
     std::size_t t1 = h(1);
     std::size_t tn1 = h(-1);
     std::size_t pinf = h(INFINITY);
     std::size_t ninf = h(-INFINITY);
     assert(t0 == tn0);
     assert(t0 != tp1);
     assert(t0 != t1);
     assert(t0 != tn1);