bug#62604: clarify that libtool is not MT-safe regardless of the underlying system

[Barnabás Pőcze]

To whom it may concern,


The libtool documentation states:

  If you wish to use libltdl in a multithreaded environment, then you must
  mutex lock around libltdl calls, since they may in turn be calling
  non-thread-safe system calls on some target hosts. 
  
  
(https://www.gnu.org/software/libtool/manual/libtool.html#Thread-Safety-in-libltdl)

which to me seems to imply that if the underlying system is thread-safe,
then libtool is also thread-safe. But this cannot be the case because libtool
- as far as I understand - uses a global unsychronized list for storing handles.

See https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/2834 as well.


Regards,
Barnabás Pőcze