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/interpreter/wasm.h

@@ -369,6 +369,13 @@ typedef struct WASMCustomSection {
 #if WASM_ENABLE_JIT != 0
 struct AOTCompData;
 struct AOTCompContext;
+
+/* Orc JIT thread arguments */
+typedef struct OrcJitThreadArg {
+    struct AOTCompContext *comp_ctx;
+    struct WASMModule *module;
+    uint32 group_idx;
+} OrcJitThreadArg;
 #endif
 
 struct WASMModule {
@@ -501,14 +508,20 @@ struct WASMModule {
 #endif
 
 #if WASM_ENABLE_FAST_JIT != 0
-    /* point to JITed functions */
+    /* func pointers of Fast JITed (un-imported) functions */
     void **fast_jit_func_ptrs;
 #endif
 
 #if WASM_ENABLE_JIT != 0
     struct AOTCompData *comp_data;
     struct AOTCompContext *comp_ctx;
+    /* func pointers of LLVM JITed (un-imported) functions */
     void **func_ptrs;
+    /* whether the func pointers are compiled */
+    bool *func_ptrs_compiled;
+    bool orcjit_stop_compiling;
+    korp_tid orcjit_threads[WASM_ORC_JIT_BACKEND_THREAD_NUM];
+    OrcJitThreadArg orcjit_thread_args[WASM_ORC_JIT_BACKEND_THREAD_NUM];
 #endif
 };