[loong64][mips] Fix compilation error with gcc

SimulatorBase::ConvertArg should be a protect member so that
CallArgument::CallArgument can access it.

Change-Id: I60b23b45c2247cd28e73808df7b77e604d154932
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3659057Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Yu Liu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#80693}

src/execution/simulator-base.h

@@ -88,13 +88,6 @@ class SimulatorBase {
   static typename std::enable_if<std::is_void<T>::value, T>::type ConvertReturn(
       intptr_t ret) {}
 
- private:
-  static base::Mutex* redirection_mutex_;
-  static Redirection* redirection_;
-
-  static base::Mutex* i_cache_mutex_;
-  static base::CustomMatcherHashMap* i_cache_;
-
   // Helper methods to convert arbitrary integer or pointer arguments to the
   // needed generic argument type intptr_t.
 
@@ -128,6 +121,13 @@ class SimulatorBase {
       ConvertArg(T arg) {
     UNREACHABLE();
   }
+
+ private:
+  static base::Mutex* redirection_mutex_;
+  static Redirection* redirection_;
+
+  static base::Mutex* i_cache_mutex_;
+  static base::CustomMatcherHashMap* i_cache_;
 };
 
 // When the generated code calls an external reference we need to catch that in