pylibfdt: fix swig build in install

A 'pip install' is silently broken unless the tree is dirty and contains
pylibfdt/libfdt.py. The problem is a known issue[1] with SWIG and
setuptools where the 'build_py' stage needing module.py runs before
the 'build_ext' stage which generates it. The work-around is to override
'build_py' to run 'build_ext' first.

[1] https://stackoverflow.com/questions/50239473/building-a-module-with-setuptools-and-swig

Signed-off-by: Rob Herring <robh@kernel.org>
Message-Id: <20220203180408.611645-2-robh@kernel.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

MANIFEST.in

@@ -6,7 +6,6 @@ include GPL
 include BSD-2-Clause
 include setup.py
 include pylibfdt/libfdt.i
-include pylibfdt/*.py
 include libfdt/libfdt.h
 include libfdt/fdt.h
 include libfdt/libfdt_env.h

setup.py

@@ -11,6 +11,8 @@ Written by Simon Glass <sjg@chromium.org>
 """
 
 from setuptools import setup, Extension
+from setuptools.command.build_py import build_py as _build_py
+
 import os
 import re
 import sys
@@ -40,11 +42,17 @@ libfdt_module = Extension(
     swig_opts=['-I' + os.path.join(srcdir, 'libfdt')],
 )
 
+class build_py(_build_py):
+    def run(self):
+        self.run_command("build_ext")
+        return super().run()
+
 setup(
     name='libfdt',
     use_scm_version={
         "root": srcdir,
     },
+    cmdclass = {'build_py' : build_py},
     setup_requires = ['setuptools_scm'],
     author='Simon Glass',
     author_email='sjg@chromium.org',