Build against system net-libs/llhttp: the GitHub tarball leaves the llhttp
submodule empty, so its sources and license file are not available.

--- a/setup.py
+++ b/setup.py
@@ -5,14 +5,11 @@
     "geventhttpclient._parser",
     sources=[
         "ext/_parser.c",
-        "llhttp/src/api.c",
-        "llhttp/src/http.c",
-        "llhttp/src/llhttp.c",
     ],
     include_dirs=[
         "ext",
-        "llhttp/include",
     ],
+    libraries=["llhttp"],
 )
 
 setup(
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -9,7 +9,7 @@
 readme = "README.md"
 requires-python = ">=3.11"
 license = "MIT"
-license-files = ["LICENSE-MIT", "llhttp/LICENSE"]
+license-files = ["LICENSE-MIT"]
 keywords = ["http", "gevent", "client"]
 authors = [{name = "Antonin Amand", email = "antonin.amand@gmail.com"}]
 classifiers = [