Add parallel compile from pybind11

Author: wiredfool

pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 build-backend = "backend"
 requires = [
+  "pybind11",
   "setuptools>=77",
 ]
 backend-path = [

setup.py

@@ -18,9 +18,12 @@
 from collections.abc import Iterator
 from typing import Any
 
+from pybind11.setup_helpers import ParallelCompile
 from setuptools import Extension, setup
 from setuptools.command.build_ext import build_ext
 
+ParallelCompile("MAX_CONCURRENCY", default=0).install()
+
 
 def get_version() -> str:
     version_file = "src/PIL/_version.py"
@@ -1048,12 +1051,12 @@ def debug_build() -> bool:
     Extension("PIL._imagingmorph", ["src/_imagingmorph.c"]),
 ]
 
-
 # parse configuration from _custom_build/backend.py
 while sys.argv[-1].startswith("--pillow-configuration="):
     _, key, value = sys.argv.pop().split("=", 2)
     configuration.setdefault(key, []).append(value)
 
+
 try:
     setup(
         cmdclass={"build_ext": pil_build_ext},