PEP 517 build in presence of --global-option emits a warning

So these are not ignored silently.

news/9774.feature.rst

@@ -1,2 +1,3 @@
 Warn instead of erroring out when doing a PEP 517 build in presence of
-``--build-option``.
+``--build-option``. Warn when doing a PEP 517 build in presence of
+``--global-option``.

src/pip/_internal/wheel_builder.py

@@ -244,6 +244,10 @@ def _build_one_inside_env(
         if req.use_pep517:
             assert req.metadata_directory
             assert req.pep517_backend
+            if global_options:
+                logger.warning(
+                    'Ignoring --global-option when building %s using PEP 517', req.name
+                )
             if build_options:
                 logger.warning(
                     'Ignoring --build-option when building %s using PEP 517', req.name

tests/functional/test_pep517.py

@@ -266,3 +266,17 @@ def test_pep517_and_build_options(script, tmpdir, data, common_wheels):
     )
     assert 'Ignoring --build-option when building' in result.stderr
     assert 'using PEP 517' in result.stderr
+
+
+@pytest.mark.network
+def test_pep517_and_global_options(script, tmpdir, data, common_wheels):
+    """Backend generated requirements are installed in the build env"""
+    project_dir, name = make_pyproject_with_setup(tmpdir)
+    result = script.pip(
+        'wheel', '--wheel-dir', tmpdir,
+        '--global-option', 'foo',
+        '-f', common_wheels,
+        project_dir,
+    )
+    assert 'Ignoring --global-option when building' in result.stderr
+    assert 'using PEP 517' in result.stderr