fix dead recursion when __NATIVE_USE_KLIB__ is defined

klib/src/stdlib.c

@@ -30,7 +30,13 @@ int atoi(const char* nptr) {
 }
 
 void *malloc(size_t size) {
+  // On native, malloc() will be called during initializaion of C runtime.
+  // Therefore do not call panic() here, else it will yield a dead recursion:
+  //   panic() -> putchar() -> (glibc) -> malloc() -> panic()
+#if !(defined(__ISA_NATIVE__) && defined(__NATIVE_USE_KLIB__))
   panic("Not implemented");
+#endif
+  return NULL;
 }
 
 void free(void *ptr) {