speccpu/x264: recompiled mc accept Mapping

src/speccpu/x264.py

@@ -1,6 +1,6 @@
 import importlib.resources
-import os
 import shutil
+from collections.abc import Mapping
 from pathlib import Path
 from subprocess import run
 
@@ -156,7 +156,7 @@ def make(build, spec_env):
     return build_exe
 
 
-def recompile_mc(mc_path: Path, build: Path, spec_env: os._Environ):
+def recompile_mc(mc_path: Path, build: Path, spec_env: Mapping[str, str]):
     # Recompile mc.o
     mc_o_path = mc_path.with_suffix(".o")
     if mc_o_path.exists():
@@ -166,6 +166,7 @@ def recompile_mc(mc_path: Path, build: Path, spec_env: os._Environ):
     # Run "make"
     return make(build, spec_env)
 
+
 specinvoke_args = {
     "ref": [
         "--seek",