Use builtin for comparisons on x64

Author: mborland

include/boost/int128/detail/int128_imp.hpp

@@ -376,7 +376,7 @@ constexpr bool operator!=(const detail::builtin_u128 lhs, const int128_t rhs) no
 constexpr bool operator<(const int128_t lhs, const int128_t rhs) noexcept
 {
     // On ARM macs only with the clang compiler is casting to __int128 uniformly better (and seemingly cost free)
-    #if defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)
+    #if (defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)) || (defined(__x86_64__))
 
     return static_cast<detail::builtin_i128>(lhs) < static_cast<detail::builtin_i128>(rhs);
 
@@ -442,7 +442,7 @@ constexpr bool operator<(const detail::builtin_u128 lhs, const int128_t rhs) noe
 constexpr bool operator>(const int128_t lhs, const int128_t rhs) noexcept
 {
     // On ARM macs only with the clang compiler is casting to __int128 uniformly better (and seemingly cost free)
-    #if defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)
+    #if (defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)) || (defined(__x86_64__))
 
     return static_cast<detail::builtin_i128>(lhs) > static_cast<detail::builtin_i128>(rhs);
 
@@ -508,7 +508,7 @@ constexpr bool operator>(const detail::builtin_u128 lhs, const int128_t rhs) noe
 constexpr bool operator<=(const int128_t lhs, const int128_t rhs) noexcept
 {
     // On ARM macs only with the clang compiler is casting to __int128 uniformly better (and seemingly cost free)
-    #if defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)
+    #if (defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)) || (defined(__x86_64__))
 
     return static_cast<detail::builtin_i128>(lhs) <= static_cast<detail::builtin_i128>(rhs);
 
@@ -574,7 +574,7 @@ constexpr bool operator<=(const detail::builtin_u128 lhs, const int128_t rhs) no
 constexpr bool operator>=(const int128_t lhs, const int128_t rhs) noexcept
 {
     // On ARM macs only with the clang compiler is casting to __int128 uniformly better (and seemingly cost free)
-    #if defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)
+    #if (defined(__aarch64__) && defined(__APPLE__) && defined(__clang__)) || (defined(__x86_64__))
 
     return static_cast<detail::builtin_i128>(lhs) >= static_cast<detail::builtin_i128>(rhs);