work around gcc 8.2.1+ bug #89303

Do not call std::make_shared on classes inheriting from
std::enable_shared_from_this when compiling with g++ 8.2.

* NEWS: Mention the bug.
* spot/misc/common.hh (SPOT_make_shared_enabled__): New macro.
* spot/twa/twagraph.cc, spot/twa/twagraph.hh, spot/twa/twaproduct.hh,
spot/twa/taatgba.hh, spot/twaalgos/couvreurnew.cc,
spot/twaalgos/magic.cc, spot/twaalgos/se05.cc, spot/twaalgos/tau03.cc,
spot/twaalgos/tau03opt.cc, spot/twaalgos/gv04.cc,
spot/ltsmin/ltsmin.cc, spot/twaalgos/gtec/gtec.cc: Use it.

NEWS

@@ -1,5 +1,11 @@
 New in spot 2.7.0.dev (not yet release)
 
+  Build
+
+  - Work around GCC bug #89303, that causes memory leaks and std::weak_bad_ptr
+    exceptions when Spot is compiled with the version of g++ 8.2 currently
+    distributed with Debian (starting with 8.2.0-15).
+
   Python:
 
   - The following methods of spot::bdd_dict are now usable in Python when