Fix Windows ninja builds when MAX_JOBS is specified (pytorch#65444)

Summary:
Reported by cloudhan in pytorch#64733 (comment)

Fixes regression introduced by pytorch@047e682

cc malfet seemethere

Pull Request resolved: pytorch#65444

Reviewed By: dagitses, seemethere

Differential Revision: D31103260

Pulled By: malfet

fbshipit-source-id: 9d5454a64cb8a0b96264119cf16582cc5afed284

tools/setup_helpers/cmake.py

@@ -387,7 +387,7 @@ def build(self, my_env: Dict[str, str]) -> None:
             # then. Until then, we use "--" to pass parameters to the
             # underlying build system.
             build_args += ['--']
-            if IS_WINDOWS:
+            if IS_WINDOWS and not USE_NINJA:
                 # We are likely using msbuild here
                 build_args += ['/p:CL_MPCount={}'.format(max_jobs)]
             else:

tools/test/test_cmake.py

@@ -22,7 +22,11 @@ def test_build_jobs(self, mock_cpu_count: unittest.mock.MagicMock) -> None:
             # MAX_JOBS, USE_NINJA, IS_WINDOWS,         want
             ((     '8',      True,     False),          ['-j', '8']),  # noqa: E201,E241
             ((    None,      True,     False),                 None),  # noqa: E201,E241
+            ((     '7',     False,     False),          ['-j', '7']),  # noqa: E201,E241
+            ((    None,     False,     False),         ['-j', '13']),  # noqa: E201,E241
+            ((     '6',      True,      True),          ['-j', '6']),  # noqa: E201,E241
             ((    None,      True,      True),                 None),  # noqa: E201,E241
+            ((    '11',     False,      True), ['/p:CL_MPCount=11']),  # noqa: E201,E241
             ((    None,     False,      True), ['/p:CL_MPCount=13']),  # noqa: E201,E241
         ]
         for (max_jobs, use_ninja, is_windows), want in cases: