setup.py: improve autotools glue

autoreconf may successfully run autoconf but not automake, so we should
check that Makefile.in exists, not configure. Additionally, there also
seem to be some cases where configure fails but Makefile is still
generated. Make sure we delete the potentially-broken output if
autoreconf/configure failed.

setup.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+import contextlib
 import re
 import os.path
 from distutils.dir_util import mkpath
@@ -24,15 +25,28 @@ class my_build_ext(build_ext):
     help_options = []
 
     def _run_autotools(self):
-        if not os.path.exists('libdrgn/configure'):
+        makefile_in = 'libdrgn/Makefile.in'
+        if not os.path.exists(makefile_in):
+            try:
                 subprocess.check_call(['autoreconf', '-i', 'libdrgn'])
+            except Exception:
+                with contextlib.suppress(FileNotFoundError):
+                    os.remove(makefile_in)
+                raise
+
         mkpath(self.build_temp)
-        if not os.path.exists(os.path.join(self.build_temp, 'Makefile')):
+        makefile = os.path.join(self.build_temp, 'Makefile')
+        if not os.path.exists(makefile):
             args = [
                 os.path.relpath('libdrgn/configure', self.build_temp),
                 '--disable-static', '--with-python=' + sys.executable,
             ]
+            try:
                 subprocess.check_call(args, cwd=self.build_temp)
+            except Exception:
+                with contextlib.suppress(FileNotFoundError):
+                    os.remove(makefile)
+                raise
 
     def get_source_files(self):
         self._run_autotools()