Refactor Orc JIT to enable lazy compilation (#974)

Refactor LLVM Orc JIT to actually enable the lazy compilation and speedup
the launching process:
  https://llvm.org/docs/ORCv2.html#laziness

Main modifications:
- Create LLVM module for each wasm function, wrap it with thread safe module
  so that the modules can be compiled parallelly
- Lookup function from aot module instance's func_ptrs but not directly call the
  function to decouple the module relationship
- Compile the function when it is first called and hasn't been compiled
- Create threads to pre-compile the WASM functions parallelly when loading
- Set Lazy JIT as default, update document and build/test scripts

core/iwasm/common/wasm_runtime_common.c

@@ -1307,7 +1307,7 @@ wasm_runtime_finalize_call_function(WASMExecEnv *exec_env,
     uint32 argv_i = 0, result_i = 0, ret_argv_i = 0;
     WASMType *func_type;
 
-    bh_assert(argv && ret_argv);
+    bh_assert((argv && ret_argv) || (argc == 0));
 
     if (argv == ret_argv) {
         return true;