Add ADX detection

Author: mborland

include/boost/decimal/detail/config.hpp

@@ -90,6 +90,11 @@
 #    include <x86intrin.h>
 #  endif
 #  define BOOST_DECIMAL_HAS_X64_INTRINSICS
+#  ifdef __ADX__
+#    define BOOST_DECIMAL_ADD_CARRY _addcarryx_u64
+#  else
+#    define BOOST_DECIMAL_ADD_CARRY _addcarry_u64
+#  endif
 #elif defined(__ARM_NEON__)
 #  ifndef BOOST_DECIMAL_BUILD_MODULE
 #    include <arm_neon.h>

include/boost/decimal/detail/emulated128.hpp

@@ -764,8 +764,8 @@ constexpr auto operator+(uint128 lhs, uint128 rhs) noexcept -> uint128
         unsigned long long low {};
         unsigned long long high {};
 
-        const auto carry {_addcarryx_u64(0, lhs.low, rhs.low, &low)};
-        _addcarryx_u64(carry, lhs.high, rhs.high, &high);
+        const auto carry {BOOST_DECIMAL_ADD_CARRY(0, lhs.low, rhs.low, &low)};
+        BOOST_DECIMAL_ADD_CARRY(carry, lhs.high, rhs.high, &high);
 
         return uint128{high, low};
     }