Phase 22.x WIP: LLVM backend improvements + MIR builder enhancements

LLVM backend improvements:
- Add native LLVM backend support (NYASH_LLVM_BACKEND=native)
- Add crate backend selector with priority (crate > llvmlite)
- Add native_llvm_builder.py for native IR generation
- Add NYASH_LLVM_NATIVE_TRACE=1 for IR dump

MIR builder enhancements:
- Refactor lower_if_compare_* boxes for better code generation
- Refactor lower_return_* boxes for optimized returns
- Refactor lower_loop_* boxes for loop handling
- Refactor lower_method_* boxes for method calls
- Update pattern_util_box for better pattern matching

Smoke tests:
- Add phase2100 S3 backend selector tests (17 new tests)
- Add phase2120 native backend tests (4 new tests)
- Add phase2034 MIR builder internal tests (2 new tests)
- Add phase2211 TLV shim parity test

Documentation:
- Update ENV_VARS.md with LLVM backend variables
- Update CURRENT_TASK.md with progress
- Update README.md and CHANGELOG.md

Config:
- Add NYASH_LLVM_BACKEND env support in src/config/env.rs
- Update ny_mir_builder.sh for backend selection
- Update dispatch.rs for backend routing

Tools:
- Add tools/native_llvm_builder.py
- Update smokes/v2/profiles/quick/core/phase2100/run_all.sh

Known: Many Hako builder internal files modified for optimization

src/config/env.rs

@@ -33,9 +33,12 @@ impl NyashEnv {
 
 // Global current env config (thread-safe)
 use once_cell::sync::OnceCell;
+use std::collections::HashSet;
+use std::sync::Mutex;
 use std::sync::RwLock;
 
 static GLOBAL_ENV: OnceCell<RwLock<NyashEnv>> = OnceCell::new();
+static WARNED_ALIASES: OnceCell<Mutex<HashSet<String>>> = OnceCell::new();
 // フェーズM.2: PHI_ON_GATED_WARNED削除（phi-legacy簡略化により不要）
 
 pub fn current() -> NyashEnv {
@@ -376,11 +379,19 @@ pub fn cli_verbose() -> bool {
 }
 pub fn enable_using() -> bool {
     // Phase 15: デフォルトON（using systemはメイン機能）
-    // NYASH_ENABLE_USING=0 で明示的に無効化可能
+    // NYASH_ENABLE_USING=0 で明示的に無効化可能。HAKO_ENABLE_USING は互換のため受理（警告）。
     match std::env::var("NYASH_ENABLE_USING").ok().as_deref() {
-        Some("0") | Some("false") | Some("off") => false,
-        _ => true, // デフォルト: ON
+        Some("0") | Some("false") | Some("off") => return false,
+        Some(_) => return true,
+        None => {}
     }
+    // Fallback to alias
+    if let Some(v) = std::env::var("HAKO_ENABLE_USING").ok() {
+        warn_alias_once("HAKO_ENABLE_USING", "NYASH_ENABLE_USING");
+        let lv = v.to_ascii_lowercase();
+        return !(lv == "0" || lv == "false" || lv == "off");
+    }
+    true // default ON
 }
 
 // ---- Using profiles (dev|ci|prod) ----
@@ -466,7 +477,14 @@ pub fn ny_compiler_stage3() -> bool {
 /// When enabled, the Rust parser accepts Stage-3 surface (try/catch/finally, throw).
 /// Default is OFF to keep Stage-2 stable.
 pub fn parser_stage3() -> bool {
-    std::env::var("NYASH_PARSER_STAGE3").ok().as_deref() == Some("1")
+    if std::env::var("NYASH_PARSER_STAGE3").ok().as_deref() == Some("1") {
+        return true;
+    }
+    if std::env::var("HAKO_PARSER_STAGE3").ok().as_deref() == Some("1") {
+        warn_alias_once("HAKO_PARSER_STAGE3", "NYASH_PARSER_STAGE3");
+        return true;
+    }
+    false
 }
 
 /// Parser gate for Block‑Postfix Catch acceptance
@@ -578,3 +596,72 @@ pub fn oob_strict_fail() -> bool {
         .or_else(|| env_flag("NYASH_OOB_STRICT_FAIL"))
         .unwrap_or(false)
 }
+
+/// Primary verification route: return true when Hakorune VM is requested as primary.
+/// Accepts HAKO_VERIFY_PRIMARY=hakovm (preferred) or legacy HAKO_ROUTE_HAKOVM=1 (deprecated, warns).
+pub fn verify_primary_is_hakovm() -> bool {
+    if std::env::var("HAKO_VERIFY_PRIMARY").ok().as_deref() == Some("hakovm") {
+        return true;
+    }
+    if env_bool("HAKO_ROUTE_HAKOVM") {
+        warn_alias_once("HAKO_ROUTE_HAKOVM", "HAKO_VERIFY_PRIMARY=hakovm");
+        return true;
+    }
+    false
+}
+
+fn warn_alias_once(alias: &str, primary: &str) {
+    let set = WARNED_ALIASES.get_or_init(|| Mutex::new(HashSet::new()));
+    if let Ok(mut s) = set.lock() {
+        if !s.contains(alias) {
+            eprintln!("[deprecate/env] '{}' is deprecated; use '{}'", alias, primary);
+            s.insert(alias.to_string());
+        }
+    }
+}
+
+// ---- ENV consolidation helpers (Phase 21.10/22.1) ----
+/// LLVM opt level (primary: NYASH_LLVM_OPT_LEVEL; alias: HAKO_LLVM_OPT_LEVEL)
+/// Returns string level (e.g., "0", "1", ...). Default: "0" when unset.
+pub fn llvm_opt_level() -> String {
+    if let Some(v) = std::env::var("NYASH_LLVM_OPT_LEVEL").ok() {
+        return v;
+    }
+    if let Some(v) = std::env::var("HAKO_LLVM_OPT_LEVEL").ok() {
+        warn_alias_once("HAKO_LLVM_OPT_LEVEL", "NYASH_LLVM_OPT_LEVEL");
+        return v;
+    }
+    "0".to_string()
+}
+
+/// Gate‑C(Core) route request (primary: NYASH_GATE_C_CORE; alias: HAKO_GATE_C_CORE)
+pub fn gate_c_core() -> bool {
+    if env_bool("NYASH_GATE_C_CORE") { return true; }
+    if env_bool("HAKO_GATE_C_CORE") {
+        warn_alias_once("HAKO_GATE_C_CORE", "NYASH_GATE_C_CORE");
+        return true;
+    }
+    false
+}
+
+/// Consolidated toggle for selfhost NY compiler pipeline.
+/// Primary: NYASH_USE_NY_COMPILER=0|1. Legacy disables accepted (with warning):
+/// NYASH_DISABLE_NY_COMPILER/HAKO_DISABLE_NY_COMPILER (any true value disables).
+pub fn use_ny_compiler() -> bool {
+    // Primary knob takes precedence when explicitly set
+    if let Some(v) = std::env::var("NYASH_USE_NY_COMPILER").ok() {
+        let lv = v.trim().to_ascii_lowercase();
+        return lv == "1" || lv == "true" || lv == "on";
+    }
+    // Legacy disable aliases — if any is true, treat as disabled and warn
+    if env_bool("NYASH_DISABLE_NY_COMPILER") {
+        warn_alias_once("NYASH_DISABLE_NY_COMPILER", "NYASH_USE_NY_COMPILER=0");
+        return false;
+    }
+    if env_bool("HAKO_DISABLE_NY_COMPILER") {
+        warn_alias_once("HAKO_DISABLE_NY_COMPILER", "NYASH_USE_NY_COMPILER=0");
+        return false;
+    }
+    // Default: ON (MVP selfhost path)
+    true
+}