fix: make scalar fms fused (std::fma(a, b, -c))

Author: DiamonDinoia

include/xsimd/arch/xsimd_scalar.hpp

@@ -954,11 +954,17 @@ namespace xsimd
     }
 
     template <class T>
-    XSIMD_INLINE std::enable_if_t<std::is_scalar_v<T>, T> fms(const T& a, const T& b, const T& c) noexcept
+    XSIMD_INLINE std::enable_if_t<std::is_integral_v<T>, T> fms(const T& a, const T& b, const T& c) noexcept
     {
         return a * b - c;
     }
 
+    template <class T>
+    XSIMD_INLINE std::enable_if_t<std::is_floating_point_v<T>, T> fms(const T& a, const T& b, const T& c) noexcept
+    {
+        return std::fma(a, b, -c);
+    }
+
     namespace detail
     {
         template <class C>