Merge pull request #3733 from WalterBright/fix22553

fix Issue 22553 - ImportC: undefined identifier __uint128_t

src/__builtins.di

@@ -91,4 +91,12 @@ version (DigitalMars)
     int   __builtin_constant_p(T)(T exp) { return 0; } // should be something like __traits(compiles, enum X = expr)
     long  __builtin_expect()(long exp, long c) { return exp; }
     void* __builtin_assume()(const void* p, size_t align_, ...) { return cast(void*)p; }
+
+    /* Header on macOS for arm64 references this.
+     * Don't need to implement it, it just needs to compile
+     */
+    align (16) struct __uint128_t
+    {
+        ulong a, b;
+    }
 }