Implement the segue optimization for LLVM AOT/JIT (#2230)

Segue is an optimization technology which uses x86 segment register to store
the WebAssembly linear memory base address, so as to remove most of the cost
of SFI (Software-based Fault Isolation) base addition and free up a general
purpose register, by this way it may:
- Improve the performance of JIT/AOT
- Reduce the footprint of JIT/AOT, the JIT/AOT code generated is smaller
- Reduce the compilation time of JIT/AOT

This PR uses the x86-64 GS segment register to apply the optimization, currently
it supports linux and linux-sgx platforms on x86-64 target. By default it is disabled,
developer can use the option below to enable it for wamrc and iwasm(with LLVM
JIT enabled):
```bash
wamrc --enable-segue=[<flags>] -o output_file wasm_file
iwasm --enable-segue=[<flags>] wasm_file [args...]
```
`flags` can be:
    i32.load, i64.load, f32.load, f64.load, v128.load,
    i32.store, i64.store, f32.store, f64.store, v128.store
Use comma to separate them, e.g. `--enable-segue=i32.load,i64.store`,
and `--enable-segue` means all flags are added.

Acknowledgement:
Many thanks to Intel Labs, UC San Diego and UT Austin teams for introducing this
technology and the great support and guidance!

Signed-off-by: Wenyong Huang <wenyong.huang@intel.com>
Co-authored-by: Vahldiek-oberwagner, Anjo Lucas <anjo.lucas.vahldiek-oberwagner@intel.com>

core/iwasm/aot/aot_runtime.c

@@ -1015,6 +1015,15 @@ execute_post_instantiate_functions(AOTModuleInstance *module_inst,
         }
     }
 
+#if defined(os_writegsbase)
+    {
+        AOTMemoryInstance *memory_inst = aot_get_default_memory(module_inst);
+        if (memory_inst)
+            /* write base addr of linear memory to GS segment register */
+            os_writegsbase(memory_inst->memory_data);
+    }
+#endif
+
     /* Execute start function for both main insance and sub instance */
     if (module->start_function) {
         AOTFunctionInstance start_func = { 0 };
@@ -1453,6 +1462,15 @@ aot_call_function(WASMExecEnv *exec_env, AOTFunctionInstance *function,
     }
     argc = func_type->param_cell_num;
 
+#if defined(os_writegsbase)
+    {
+        AOTMemoryInstance *memory_inst = aot_get_default_memory(module_inst);
+        if (memory_inst)
+            /* write base addr of linear memory to GS segment register */
+            os_writegsbase(memory_inst->memory_data);
+    }
+#endif
+
     /* func pointer was looked up previously */
     bh_assert(function->u.func.func_ptr != NULL);