Refactor app heap and memory boundary check, and fix os_printf compilation error (#356)

Insert app heap before __heap_base, or before new page
Fix os_printf compilation error in some platforms

samples/wasm-c-api/src/callback.c

@@ -68,7 +68,11 @@ int main(int argc, const char* argv[]) {
 
   // Load binary.
   printf("Loading binary...\n");
+#if WASM_ENABLE_AOT != 0 && WASM_ENABLE_INTERP == 0
+  FILE* file = fopen("callback.aot", "rb");
+#else
   FILE* file = fopen("callback.wasm", "rb");
+#endif
   if (!file) {
     printf("> Error loading module!\n");
     return 1;