[3.7] bpo-32647: Link ctypes extension with libdl. (GH-5550) (#5874)

The ctypes module used to depend on indirect linking for dlopen. The shared extension is now explicitly linked against libdl on platforms with dl. Signed-off-by: Christian Heimes <christian@python.org> (cherry picked from commit 5bb9692) Co-authored-by: Christian Heimes <christian@python.org>

Author: miss-islington

Misc/NEWS.d/next/Library/2018-02-05-13-31-42.bpo-32647.ktmfR_.rst

@@ -0,0 +1,2 @@
+The ctypes module used to depend on indirect linking for dlopen. The shared
+extension is now explicitly linked against libdl on platforms with dl.

setup.py

@@ -2005,6 +2005,10 @@ def detect_ctypes(self, inc_dirs, lib_dirs):
  ext.libraries.append(ffi_lib)
  self.use_system_libffi = True
 
+ if sysconfig.get_config_var('HAVE_LIBDL'):
+ # for dlopen, see bpo-32647
+ ext.libraries.append('dl')
+
  def _decimal_ext(self):
  extra_compile_args = []
  undef_macros = []