Issue #9516: avoid errors in sysconfig when MACOSX_DEPLOYMENT_TARGET is set in shell.

Without this patch python will fail to start properly when the environment
variable MACOSX_DEPLOYMENT_TARGET is set on MacOSX and has a value that is
not compatible with the value during Python's build. This is caused by code
in sysconfig that was only meant to be used in disutils.

Lib/distutils/tests/test_build_ext.py

@@ -2,6 +2,7 @@ import sys
 import os
 import shutil
 from io import StringIO
+import textwrap
 
 from distutils.core import Distribution
 from distutils.command.build_ext import build_ext
@@ -419,6 +420,67 @@ class BuildExtTestCase(TempdirManager,
         wanted = os.path.join(curdir, 'twisted', 'runner', 'portmap' + ext)
         self.assertEqual(wanted, path)
 
+
+    @unittest.skipUnless(sys.platform == 'darwin', 'test only relevant for MacOSX')
+    def test_deployment_target(self):
+        self._try_compile_deployment_target()
+
+        orig_environ = os.environ
+        os.environ = orig_environ.copy()
+        self.addCleanup(setattr, os, 'environ', orig_environ)
+
+        os.environ['MACOSX_DEPLOYMENT_TARGET']='10.1'
+        self._try_compile_deployment_target()
+
+
+    def _try_compile_deployment_target(self):
+        deptarget_c = os.path.join(self.tmp_dir, 'deptargetmodule.c')
+
+        with open(deptarget_c, 'w') as fp:
+            fp.write(textwrap.dedent('''\
+                #include <AvailabilityMacros.h>
+
+                int dummy;
+
+                #if TARGET != MAC_OS_X_VERSION_MIN_REQUIRED
+                #error "Unexpected target"
+                #endif
+
+            '''))
+
+        target = sysconfig.get_config_var('MACOSX_DEPLOYMENT_TARGET')
+        target = tuple(map(int, target.split('.')))
+        target = '%02d%01d0' % target
+
+        deptarget_ext = Extension(
+            'deptarget',
+            [deptarget_c],
+            extra_compile_args=['-DTARGET=%s'%(target,)],
+        )
+        dist = Distribution({
+            'name': 'deptarget',
+            'ext_modules': [deptarget_ext]
+        })
+        dist.package_dir = self.tmp_dir
+        cmd = build_ext(dist)
+        cmd.build_lib = self.tmp_dir
+        cmd.build_temp = self.tmp_dir
+
+        try:
+            old_stdout = sys.stdout
+            if not support.verbose:
+                # silence compiler output
+                sys.stdout = StringIO()
+            try:
+                cmd.ensure_finalized()
+                cmd.run()
+            finally:
+                sys.stdout = old_stdout
+
+        except CompileError:
+            self.fail("Wrong deployment target during compilation")
+
+
 def test_suite():
     src = _get_source_filename()
     if not os.path.exists(src):