add constructor syntax workaround for msvc

Author: cmazakas

include/boost/hash2/xxh3.hpp

@@ -537,10 +537,8 @@ class xxh3_128
 
 private: // supporting constructor for the static factory functions
 
-    BOOST_CXX14_CONSTEXPR xxh3_128( std::uint64_t seed, unsigned char const* p, std::size_t n ): seed_( seed )
+    BOOST_CXX14_CONSTEXPR xxh3_128( std::uint64_t seed, unsigned char const* p, std::size_t n, bool with_secret ): seed_( seed ), with_secret_( with_secret )
     {
-        with_secret_ = true;
-
         if( n < min_secret_len )
         {
             // this is a precondition violation for XXH3, but we try to do something reasonable
@@ -612,7 +610,7 @@ class xxh3_128
 
     static BOOST_CXX14_CONSTEXPR xxh3_128 with_secret( unsigned char const* p, std::size_t n )
     {
-        return xxh3_128( 0, p, n );
+        return xxh3_128( 0, p, n, true );
     }
 
     static xxh3_128 with_secret( void const* p, std::size_t n )
@@ -622,11 +620,7 @@ class xxh3_128
 
     static BOOST_CXX14_CONSTEXPR xxh3_128 with_secret_and_seed( unsigned char const* p, std::size_t n, std::uint64_t seed )
     {
-        xxh3_128 r( seed, p, n );
-
-        r.with_secret_ = false;
-
-        return r;
+        return xxh3_128( seed, p, n, false );
     }
 
     static xxh3_128 with_secret_and_seed( void const* p, std::size_t n, std::uint64_t seed )