Refactor LLVM JIT (#1613)

Refactor LLVM JIT for some purposes:
- To simplify the source code of JIT compilation
- To simplify the JIT modes
- To align with LLVM latest changes
- To prepare for the Multi-tier JIT compilation, refer to #1302

The changes mainly include:
- Remove the MCJIT mode, replace it with ORC JIT eager mode
- Remove the LLVM legacy pass manager (only keep the LLVM new pass manager)
- Change the lazy mode's LLVM module/function binding:
  change each function in an individual LLVM module into all functions in a single LLVM module
- Upgraded ORC JIT to ORCv2 JIT to enable lazy compilation

Refer to #1468

core/iwasm/aot/aot_runtime.c

@@ -1321,6 +1321,9 @@ aot_call_function(WASMExecEnv *exec_env, AOTFunctionInstance *function,
     }
     argc = func_type->param_cell_num;
 
+    /* func pointer was looked up previously */
+    bh_assert(function->u.func.func_ptr != NULL);
+
     /* set thread handle and stack boundary */
     wasm_exec_env_set_thread_info(exec_env);
 
@@ -1828,6 +1831,11 @@ aot_call_indirect(WASMExecEnv *exec_env, uint32 tbl_idx, uint32 table_elem_idx,
     func_type_idx = func_type_indexes[func_idx];
     func_type = aot_module->func_types[func_type_idx];
 
+    if (func_idx >= aot_module->import_func_count) {
+        /* func pointer was looked up previously */
+        bh_assert(func_ptrs[func_idx] != NULL);
+    }
+
     if (!(func_ptr = func_ptrs[func_idx])) {
         bh_assert(func_idx < aot_module->import_func_count);
         import_func = aot_module->import_funcs + func_idx;