feat: LLVM_SYS_180_PREFIX環境変数削除完了！llvm-harness経路でRust LLVMバインディング不要化達成

🚀 Phase 15.5 MIR Call統一革命 - LLVM環境変数削除フェーズ完了

## ✅ 完了内容
- **条件分岐実装**: llvm-harness(デフォルト)はLLVM_SYS_180_PREFIX不要
- **後方互換性維持**: llvm-inkwell-legacy使用時はLLVM_SYS_180_PREFIX必要
- **全ツール統一**: 12個のビルドスクリプト・テストスクリプトを一括更新
- **ドキュメント更新**: ENV_VARS.mdでLLVM feature選択方法を明記

## 🛠️ 更新ファイル
- **コアビルド**: src/runner/build.rs, tools/build_llvm.sh, build_llvm.sh
- **スモークテスト**: tools/llvm_smoke.sh, tools/test/smoke/llvm/ir_phi_empty_check.sh
- **CI設定**: .github/workflows/min-gate.yml
- **Windows版**: build_llvm_wsl.sh, build_llvm_wsl_msvc.sh (cross-compilation)
- **開発ツール**: tools/build_compiler_exe.sh, tools/ny_mir_builder.sh
- **ドキュメント**: docs/development/runtime/ENV_VARS.md

## ⚡ 技術的成果
- **環境変数削減**: LLVM_SYS_180_PREFIX → 条件付き使用のみ
- **Python LLVM統合**: llvmliteハーネス経路でRust LLVM依存完全除去
- **ビルド簡略化**: デフォルトでllvm-config-18のみ必要
- **動作確認**: tools/llvm_smoke.sh成功 (1648バイト.oファイル生成)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tools/test/smoke/llvm/ir_phi_empty_check.sh

@@ -7,11 +7,18 @@ set -euo pipefail
 SCRIPT=${1:-apps/tests/loop_if_phi.nyash}
 
 echo "[phi-empty-check] building nyash (llvm features)" >&2
-LLVM_PREFIX=${LLVM_SYS_180_PREFIX:-$(command -v llvm-config-18 >/dev/null 2>&1 && llvm-config-18 --prefix || true)}
-if [[ -n "${LLVM_PREFIX}" ]]; then
-  LLVM_SYS_180_PREFIX="${LLVM_PREFIX}" cargo build --release --features llvm >/dev/null
+LLVM_FEATURE=${NYASH_LLVM_FEATURE:-llvm}
+if [[ "$LLVM_FEATURE" == "llvm-inkwell-legacy" ]]; then
+  # Legacy inkwell needs LLVM_SYS_180_PREFIX
+  LLVM_PREFIX=${LLVM_SYS_180_PREFIX:-$(command -v llvm-config-18 >/dev/null 2>&1 && llvm-config-18 --prefix || true)}
+  if [[ -n "${LLVM_PREFIX}" ]]; then
+    LLVM_SYS_180_PREFIX="${LLVM_PREFIX}" cargo build --release --features "${LLVM_FEATURE}" >/dev/null
+  else
+    cargo build --release --features "${LLVM_FEATURE}" >/dev/null
+  fi
 else
-  cargo build --release --features llvm >/dev/null
+  # llvm-harness (default) doesn't need LLVM_SYS_180_PREFIX
+  cargo build --release --features "${LLVM_FEATURE}" >/dev/null
 fi
 
 IR_OUT=tmp/nyash_harness.ll

tools/test/smoke/selfhost/m2_min/test.sh

@@ -6,9 +6,16 @@ source "$ROOT/tools/test/lib/shlib.sh"
 
 build_nyash_release
 
-# Skip when LLVM toolchain is not available (either llvm-config-18 or LLVM_SYS_180_PREFIX)
-if ! command -v llvm-config-18 >/dev/null 2>&1 && [[ -z "${LLVM_SYS_180_PREFIX:-}" ]]; then
-  echo "[SKIP] selfhost M2 minimal: LLVM18 not available"; exit 0
+# Skip when LLVM toolchain is not available
+if ! command -v llvm-config-18 >/dev/null 2>&1; then
+  # For llvm-harness (default), we only need llvm-config-18
+  # For llvm-inkwell-legacy, we also need LLVM_SYS_180_PREFIX
+  LLVM_FEATURE=${NYASH_LLVM_FEATURE:-llvm}
+  if [[ "$LLVM_FEATURE" == "llvm-inkwell-legacy" && -z "${LLVM_SYS_180_PREFIX:-}" ]]; then
+    echo "[SKIP] selfhost M2 minimal: LLVM18 not available for legacy inkwell"; exit 0
+  elif [[ "$LLVM_FEATURE" != "llvm-inkwell-legacy" ]]; then
+    echo "[SKIP] selfhost M2 minimal: llvm-config-18 not available"; exit 0
+  fi
 fi
 
 build_ny_llvmc || { echo "[SKIP] selfhost M2 minimal: ny-llvmc not built"; exit 0; }