bpo-36356: Fix memory leak in _PyPreConfig_Read() (GH-12425)

_PyPreConfig_Read() now free 'old_old' at exit.

Author: btharper

Misc/NEWS.d/next/Build/2019-03-18-23-49-15.bpo-36356.WNrwYI.rst

@@ -0,0 +1 @@
+Fix leaks that led to build failure when configured with address sanitizer.

Python/preconfig.c

@@ -514,6 +514,7 @@ _PyPreConfig_Read(_PyPreConfig *config)
  err = preconfig_read(config, NULL);
 
  setlocale(LC_CTYPE, old_loc);
+ PyMem_RawFree(old_loc);
 
  return err;
 }