Make {add,sub,mul}_will_overflow more compiler-independent

luna/include/luna/SafeArithmetic.h

@@ -1,21 +1,6 @@
 #pragma once
 #include <luna/Result.h>
 
-template <typename T> constexpr bool add_will_overflow(T a, T b)
-{
-    return __builtin_add_overflow_p(a, b, (T)0);
-}
-
-template <typename T> constexpr bool sub_will_overflow(T a, T b)
-{
-    return __builtin_sub_overflow_p(a, b, (T)0);
-}
-
-template <typename T> constexpr bool mul_will_overflow(T a, T b)
-{
-    return __builtin_mul_overflow_p(a, b, (T)0);
-}
-
 template <typename T> Result<T> safe_add(T a, T b)
 {
     T result;
@@ -41,4 +26,31 @@ template <typename T> Result<T> safe_mul(T a, T b)
     if (__builtin_mul_overflow(a, b, &result)) return err(EOVERFLOW);
 
     return result;
+}
+
+template <typename T> bool add_will_overflow(T a, T b)
+{
+#ifdef __GNUC__
+    return __builtin_add_overflow_p(a, b, (T)0);
+#else
+    return safe_add(a, b).has_error();
+#endif
+}
+
+template <typename T> bool sub_will_overflow(T a, T b)
+{
+#ifdef __GNUC__
+    return __builtin_sub_overflow_p(a, b, (T)0);
+#else
+    return safe_sub(a, b).has_error();
+#endif
+}
+
+template <typename T> bool mul_will_overflow(T a, T b)
+{
+#ifdef __GNUC__
+    return __builtin_mul_overflow_p(a, b, (T)0);
+#else
+    return safe_mul(a, b).has_error();
+#endif
 }