Mar 23, 2026
diff --git a/Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst b/Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst
 Fix building the jit stencils on Windows when the interpreter is built with
 a different clang version. Patch by Chris Eibl.
diff --git a/Tools/jit/_llvm.py b/Tools/jit/_llvm.py
    async with _CORES:
        if echo:
            print(shlex.join(command))

        if os.name == "nt":
            env = os.environ.copy()
            try:
                # https://github.com/python/cpython/issues/146210
                # When the Python iterpreter is built with
                # "/p:PlatformToolset=ClangCL" "/p:LLVMInstallDir=...""
                # msbuild populates the INCLUDE variable based on this
                # clang version, which might be different to the one used
                # for building the jit stencils. Mixing those include paths
                # can cause mysterious build errors, so we remove the
                # variable from the environment when invoking LLVM tools.
                del env["INCLUDE"]
            except KeyError:
                pass
        else:
            env = None
        try:
            process = await asyncio.create_subprocess_exec(
                *command, stdout=subprocess.PIPE
                *command, stdout=subprocess.PIPE, env=env
            )
        except FileNotFoundError:
            return None
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix building the jit stencils on Windows when the interpreter is built with
		a different clang version. Patch by Chris Eibl.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -42,9 +42,26 @@ async def _run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str
		async with _CORES:
		if echo:
		print(shlex.join(command))

		if os.name == "nt":
		env = os.environ.copy()
		try:
		# https://github.com/python/cpython/issues/146210
		# When the Python iterpreter is built with
		# "/p:PlatformToolset=ClangCL" "/p:LLVMInstallDir=...""
		# msbuild populates the INCLUDE variable based on this
		# clang version, which might be different to the one used
		# for building the jit stencils. Mixing those include paths
		# can cause mysterious build errors, so we remove the
		# variable from the environment when invoking LLVM tools.
		del env["INCLUDE"]
		except KeyError:
		pass
		else:
		env = None
		try:
		process = await asyncio.create_subprocess_exec(
		*command, stdout=subprocess.PIPE
		*command, stdout=subprocess.PIPE, env=env
		)
		except FileNotFoundError:
		return None
Expand Down