Fixed _sys_home computation and added diagnostics for Windows buildbot failures.

Lib/distutils/sysconfig.py

@@ -50,6 +50,8 @@ _sys_home = getattr(sys, '_home', None)
 if _sys_home and os.name == 'nt' and \
     _sys_home.lower().endswith(('pcbuild', 'pcbuild\\amd64')):
     _sys_home = os.path.dirname(_sys_home)
+    if _sys_home.endswith('pcbuild'):   # must be amd64
+        _sys_home = os.path.dirname(_sys_home)
 def _python_build():
     if _sys_home:
         return _is_python_source_dir(_sys_home)

Lib/sysconfig.py

@@ -107,7 +107,8 @@ _sys_home = getattr(sys, '_home', None)
 if _sys_home and os.name == 'nt' and \
     _sys_home.lower().endswith(('pcbuild', 'pcbuild\\amd64')):
     _sys_home = os.path.dirname(_sys_home)
-
+    if _sys_home.endswith('pcbuild'):   # must be amd64
+        _sys_home = os.path.dirname(_sys_home)
 def is_python_build(check_home=False):
     if check_home and _sys_home:
         return _is_python_source_dir(_sys_home)

Lib/test/test_venv.py

@@ -76,7 +76,10 @@ class BasicTest(BaseTest):
         data = self.get_text_file_contents(self.bindir, self.ps3name)
         self.assertTrue(data.startswith('#!%s%s' % (self.env_dir, os.sep)))
         fn = self.get_env_file(self.bindir, self.exe)
-        self.assertTrue(os.path.exists(fn), 'File %r exists' % fn)
+        if not os.path.exists(fn):  # diagnostics for Windows buildbot failures
+            print('Contents of %r:' % self.bindir)
+            print('    %r' % os.listdir(self.bindir))
+        self.assertTrue(os.path.exists(fn), 'File %r should exist.' % fn)
 
     def test_overwrite_existing(self):
         """