Fix AllocatorConfig potential SIO issue (pytorch#159629)

# Motivation
As @ScottTodd identified in this [comment](pytorch#150312 (comment)), using STL containers like `std::string` and `std::unordered_set` at static init time can cause static initialization order issues. This PR is based on and modified from his original PR: pytorch#159607. I’m stacking this PR here to help facilitate the landing and validation process.

Co-authored-by: @ScottTodd
Pull Request resolved: pytorch#159629
Approved by: https://github.com/ScottTodd, https://github.com/albanD

Author: guangyey

c10/core/AllocatorConfig.cpp

@@ -224,7 +224,7 @@ void AcceleratorAllocatorConfig::parseArgs(const std::string& env) {
       // check if the key is unrecognized.
       if (device_config_parser_hook_) {
         TORCH_CHECK(
-            keys_.find(key) != keys_.end(),
+            getKeys().find(key) != getKeys().end(),
             "Unrecognized key '",
             key,
             "' in Accelerator allocator config.");

c10/core/AllocatorConfig.h

@@ -220,11 +220,24 @@ class C10_API AcceleratorAllocatorConfig {
     return instance().last_allocator_settings_;
   }
 
+  // Use `Construct On First Use Idiom` to avoid `Static Initialization Order`
+  // issue.
+  static std::unordered_set<std::string>& getMutableKeys() {
+    static std::unordered_set<std::string> keys{
+        "max_split_size_mb",
+        "max_non_split_rounding_mb",
+        "garbage_collection_threshold",
+        "roundup_power2_divisions",
+        "expandable_segments",
+        "pinned_use_background_threads"};
+    return keys;
+  }
+
   // Returns the set of valid keys for the allocator configuration.
   // This set is used to validate the presence and correctness of keys in
   // device-specific configuration parsers.
   static const std::unordered_set<std::string>& getKeys() {
-    return keys_;
+    return getMutableKeys();
   }
 
   // Registers a device-specific configuration parser hook and its key. This
@@ -238,9 +251,10 @@ class C10_API AcceleratorAllocatorConfig {
       std::function<void(const std::string&)>&& hook,
       const std::unordered_set<std::string>& keys) {
     device_config_parser_hook_ = std::move(hook);
+    auto& mutable_keys = getMutableKeys();
     for (auto& key : keys) {
       TORCH_CHECK(
-          keys_.insert(key).second,
+          mutable_keys.insert(key).second,
           "Duplicated key '",
           key,
           "' found in device-specific configuration parser hook registration");
@@ -326,17 +340,6 @@ class C10_API AcceleratorAllocatorConfig {
   // their own environment configuration extensions.
   inline static std::function<void(const std::string&)>
       device_config_parser_hook_{nullptr};
-
-  // A set of valid configuration keys, including both common and
-  // device-specific options. This set is used to validate the presence and
-  // correctness of keys during parsing.
-  inline static std::unordered_set<std::string> keys_{
-      "max_split_size_mb",
-      "max_non_split_rounding_mb",
-      "garbage_collection_threshold",
-      "roundup_power2_divisions",
-      "expandable_segments",
-      "pinned_use_background_threads"};
 };
 
 C10_API inline void setAllocatorSettings(const std::string& env) {