1) Prepare libmpdec for the 2.4.0 release.  None of the following changes affects
   _decimal:

      o Make all "mpd_t to C integer" conversion functions available in both the
        64-bit and the 32-bit versions.

      o Make all mixed mpd_t/C integer arithmetic functions available in the
        32-bit version.

      o Better handling of __STDC_LIMIT_MACROS for C++ users.

      o Add struct tags (at the request of C++ users).

2) Check for libmpdec.so.2 if --with-system-libmpdec is used.
diff --git a/setup.py b/setup.py
index 19a7b29..9064014 100644
--- a/setup.py
+++ b/setup.py
@@ -1945,7 +1945,7 @@
         undef_macros = []
         if '--with-system-libmpdec' in sysconfig.get_config_var("CONFIG_ARGS"):
             include_dirs = []
-            libraries = ['mpdec']
+            libraries = [':libmpdec.so.2']
             sources = ['_decimal/_decimal.c']
             depends = ['_decimal/docstrings.h']
         else: