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.h

@@ -148,9 +148,9 @@ typedef struct AOTModule {
 
     /* function info */
     uint32 func_count;
-    /* point to AOTed functions */
+    /* func pointers of AOTed (un-imported) functions */
     void **func_ptrs;
-    /* function type indexes */
+    /* func type indexes of AOTed (un-imported) functions */
     uint32 *func_type_indexes;
 
     /* export info */