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/config.h

@@ -81,12 +81,26 @@
 #define WASM_ENABLE_LAZY_JIT 0
 #endif
 
-#ifndef WASM_LAZY_JIT_COMPILE_THREAD_NUM
-#define WASM_LAZY_JIT_COMPILE_THREAD_NUM 4
+#ifndef WASM_ORC_JIT_BACKEND_THREAD_NUM
+/* The number of backend threads created by runtime */
+#define WASM_ORC_JIT_BACKEND_THREAD_NUM 4
+#endif
+
+#if WASM_ORC_JIT_BACKEND_THREAD_NUM < 1
+#error "WASM_ORC_JIT_BACKEND_THREAD_NUM must be greater than 0"
+#endif
+
+#ifndef WASM_ORC_JIT_COMPILE_THREAD_NUM
+/* The number of compilation threads created by LLVM JIT */
+#define WASM_ORC_JIT_COMPILE_THREAD_NUM 4
+#endif
+
+#if WASM_ORC_JIT_COMPILE_THREAD_NUM < 1
+#error "WASM_ORC_JIT_COMPILE_THREAD_NUM must be greater than 0"
 #endif
 
 #if (WASM_ENABLE_AOT == 0) && (WASM_ENABLE_JIT != 0)
-/* LazyJIT or MCJIT can only be enabled when AOT is enabled */
+/* LLVM JIT can only be enabled when AOT is enabled */
 #undef WASM_ENABLE_JIT
 #define WASM_ENABLE_JIT 0
 
@@ -110,14 +124,6 @@
 #define WASM_ENABLE_WAMR_COMPILER 0
 #endif
 
-#if WASM_ENABLE_WAMR_COMPILER != 0
-#ifndef WASM_ENABLE_LLVM_LEGACY_PM
-/* Whether to use LLVM legacy pass manager when building wamrc,
-   by default it is disabled and LLVM new pass manager is used */
-#define WASM_ENABLE_LLVM_LEGACY_PM 0
-#endif
-#endif
-
 #ifndef WASM_ENABLE_LIBC_BUILTIN
 #define WASM_ENABLE_LIBC_BUILTIN 0
 #endif