python: drop usage of external make for extension build

This change takes advantage of setuptools build_ext feature to discover the build toolchain and acompile the extension with no hidden dependency.

Python extension can now be build and installed properly on windows when Visual C++ Build Tools are installed.

setup.py

@@ -13,26 +13,13 @@
 # limitations under the License.
 
 import os
-from setuptools import setup
+
 from setuptools import Extension
-from setuptools.command.build_ext import build_ext as BuildExt
-from subprocess import Popen
+from setuptools import setup
+from setuptools.command.build_ext import build_ext
 
 DIR = os.path.abspath(os.path.dirname(__file__))
-LIB_OBJECTS = [
-    'core/desugarer.o',
-    'core/formatter.o',
-    'core/libjsonnet.o',
-    'core/lexer.o',
-    'core/parser.o',
-    'core/pass.o',
-    'core/static_analysis.o',
-    'core/string_utils.o',
-    'core/vm.o',
-    'third_party/md5/md5.o'
-]
 
-MODULE_SOURCES = ['python/_jsonnet.c']
 
 def get_version():
     """
@@ -46,19 +33,20 @@ def get_version():
                     v_code = v_code[1:]
                 return v_code
 
-class BuildJsonnetExt(BuildExt):
-    def run(self):
-        p = Popen(['make'] + LIB_OBJECTS, cwd=DIR)
-        p.wait()
-        if p.returncode != 0:
-            raise Exception('Could not build %s' % (', '.join(LIB_OBJECTS)))
-        BuildExt.run(self)
-
 jsonnet_ext = Extension(
     '_jsonnet',
-    sources=MODULE_SOURCES,
-    extra_objects=LIB_OBJECTS,
-    include_dirs = ['include', 'third_party/md5', 'third_party/json'],
+    sources=['python/_jsonnet.c',
+             'core/desugarer.cpp',
+             'core/formatter.cpp',
+             'core/libjsonnet.cpp',
+             'core/lexer.cpp',
+             'core/parser.cpp',
+             'core/pass.cpp',
+             'core/static_analysis.cpp',
+             'core/string_utils.cpp',
+             'core/vm.cpp',
+             'third_party/md5/md5.cpp'],
+    include_dirs=['core', 'include', 'third_party/md5', 'third_party/json'],
     language='c++'
 )
 
@@ -69,8 +57,8 @@ def run(self):
       author_email='dcunnin@google.com',
       version=get_version(),
       cmdclass={
-          'build_ext': BuildJsonnetExt,
+          'build_ext': build_ext,
       },
       ext_modules=[jsonnet_ext],
       test_suite="python._jsonnet_test",
-)
+      )