lltrunc, llround: truncation in implicit conversion

[Kojoley]

Running Spirit tests that use real_concept with clang-cl yields:

In file included from C:\projects\boost\libs\spirit\test\karma\real2.cpp:7:
In file included from C:\projects\boost\libs\spirit\test\karma/real.hpp:15:
In file included from .\boost/math/concepts/real_concept.hpp:28:
.\boost/math/special_functions/round.hpp(118,12): error: implicit conversion from 'long long' to 'long double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-int-float-conversion]
   if((r > (std::numeric_limits<boost::long_long_type>::max)()) || (r < (std::numeric_limits<boost::long_long_type>::min)()))
         ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\boost/math/concepts/real_concept.hpp(297,23): note: in instantiation of function template specialization 'boost::math::llround<long double, boost::math::policies::policy<boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy> >' requested here
{ return boost::math::llround(v.value(), policies::policy<>()); }
                      ^
In file included from C:\projects\boost\libs\spirit\test\karma\real2.cpp:7:
In file included from C:\projects\boost\libs\spirit\test\karma/real.hpp:15:
In file included from .\boost/math/concepts/real_concept.hpp:29:
.\boost/math/special_functions/trunc.hpp(99,12): error: implicit conversion from 'long long' to 'long double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-int-float-conversion]
   if((r > (std::numeric_limits<boost::long_long_type>::max)()) || (r < (std::numeric_limits<boost::long_long_type>::min)()))
         ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\boost/math/concepts/real_concept.hpp(316,23): note: in instantiation of function template specialization 'boost::math::lltrunc<long double, boost::math::policies::policy<boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy> >' requested here
{ return boost::math::lltrunc(v.value(), policies::policy<>()); }
                      ^

[evanmiller]

Possible duplicate of #430 and possibly fixed by #474