add missing variadic.{c,o}

src/tests/BuildWasmApps/testassets/native-libs/variadic.c

@@ -0,0 +1,14 @@
+#include <stdarg.h>
+
+int sum(int n, ...)
+{
+    int result = 0;
+    va_list ptr;
+    va_start(ptr, n);
+
+    for (int i = 0; i < n; i++)
+        result += va_arg(ptr, int);
+
+    va_end(ptr);
+    return result;
+}