Avoid initialize LLVM repeatedly (#1671)

Currently we initialize and destroy LLVM environment in aot_create_comp_context
and aot_destroy_comp_context, which are called in wasm_module_load/unload,
and the latter may be invoked multiple times, which leads to duplicated LLVM
initialization/destroy and may result in unexpected behaviors.

Move the LLVM init/destroy into runtime init/destroy to resolve the issue.

core/iwasm/common/wasm_c_api.c

@@ -1642,9 +1642,11 @@ wasm_trap_new_internal(wasm_store_t *store,
                        const char *error_info)
 {
     wasm_trap_t *trap;
+#if WASM_ENABLE_DUMP_CALL_STACK != 0
     wasm_instance_vec_t *instances;
     wasm_instance_t *frame_instance = NULL;
     uint32 i;
+#endif
 
     if (!singleton_engine || !singleton_engine->stores
         || !singleton_engine->stores->num_elems) {