9495: Fixes issue with variadic functions on win64

src/func.c

@@ -1501,7 +1501,7 @@ void FuncDeclaration::semantic3(Scope *sc)
                         p = v_arguments;            // last parameter is _arguments[]
                     if (global.params.is64bit && global.params.isWindows)
                     {   offset += Target::ptrsize;
-                    if (p->storage_class & STClazy)
+                    if (p->storage_class & STClazy || p->type->size() > Target::ptrsize)
                         {
                             /* Necessary to offset the extra level of indirection the Win64
                              * ABI demands

test/runnable/test9495.d

@@ -0,0 +1,31 @@
+// PERMUTE_ARGS:
+
+import core.vararg;
+
+int func1(int a, ...)
+{
+  auto result = va_arg!int(_argptr);
+  return result;
+}
+
+void test9495a()
+{
+  assert(func1(5, 12345678) == 12345678);
+}
+
+int func2(const(char)[] a, ...)
+{
+  auto result = va_arg!int(_argptr);
+  return result;
+}
+
+void test9495b()
+{
+  assert(func2("5", 12345678) == 12345678);
+}
+
+void main(string[] args)
+{
+  test9495a();
+  test9495b();
+}