Add our own legacy loop unswitch pass (#1339)

Since legacy binding for loop unswitch pass was removed and we can't get
it back. Implement its equivalent in `aot_llvm_extra.cpp` and use it in
`aot_compiler.c`.

Follow up to #1183.

core/iwasm/compilation/aot_compiler.c

@@ -2643,9 +2643,8 @@ apply_func_passes(AOTCompContext *comp_ctx)
         LLVMAddLoopRotatePass(pass_mgr);
 #if LLVM_VERSION_MAJOR < 15
         LLVMAddLoopUnswitchPass(pass_mgr);
-        /* Binding disabled in LLVM 15, don't add the pass util we can either
-           add a binding to SimpleLoopUnswitchPass, or add it to
-           aot_llvm_extra.cpp */
+#else
+        aot_add_simple_loop_unswitch_pass(pass_mgr);
 #endif
         LLVMAddInstructionCombiningPass(pass_mgr);
         LLVMAddCFGSimplificationPass(pass_mgr);