OCaml 5.2.1: first release candidate

[Octachron]

This is the usual packages for the release candidate for the upcoming version 5.2.1 of OCaml.

Since this bugfix release only contains a collection of important but safe runtime fixes, this release candidate is mostly here to check that nothing has gone wrong in the 5.2 branch or in the release process.

Compared to OCaml 5.2.0, the changes in 5.2.1 are:

• 13207: Be sure to reload the register caching the exception handler in
  caml_c_call and caml_c_call_stack_args, as its value may have been changed
  if the OCaml stack is expanded during a callback.
  (Miod Vallat, report by Vesa Karvonen, review by Gabriel Scherer and
  Xavier Leroy)

• 13252: Rework register assignment in the interpreter code on m68k on Linux,
  due to the %a5 register being used by Glibc.
  (Miod Vallat, report by Stéphane Glondu, review by Gabriel Scherer and
  Xavier Leroy)

• 13268: Fix a call to test in configure.ac that was causing errors when
  LDFLAGS contains several words.
  (Stéphane Glondu, review by Miod Vallat)

• 13234, 13267: Open runtime events file in read-write mode on armel
  (armv5) systems due to atomic operations limitations on that
  platform.
  (Stéphane Glondu, review by Miod Vallat and Vincent Laviron)

• 13188: fix races in the FFI code coming from the use of Int_val(...)
  on rooted values inside blocking questions / without the runtime lock.
  (Calling Int_val(...) on non-rooted immediates is fine, but any
  access to rooted values must be done outside blocking sections /
  with the runtime lock.)
  (Etienne Millon, review by Gabriel Scherer, Jan Midtgaard, Olivier Nicole)

• 13318: Fix regression in GC alarms, and fix them for flambda.
  (Guillaume Munch-Maccagnoni, report by Benjamin Monate, review by
  Vincent Laviron and Gabriel Scherer)

• 13140: POWER back-end: fix issue with call to caml_call_realloc_stack
  from a DLL
  (Xavier Leroy, review by Miod Vallat)

• 13370: Fix a low-probability crash when calling Gc.counters.
  (Demi Marie Obenour, review by Gabriel Scherer)

• 13402, 13512, 13549, 13553: Revise bytecode implementation of callbacks
  so that it no longer produces dangling registered bytecode fragments.
  (Xavier Leroy, report by Jan Midtgaard, analysis by Stephen Dolan,
  review by Miod Vallat)

• 13502: Fix misindexing related to Gc.finalise_last that could prevent
  finalisers from being run.
  (Nick Roberts, review by Mark Shinwell)

• 13520: Fix compilation of native-code version of systhreads. Bytecode fields
  were being included in the thread descriptors.
  (David Allsopp, review by Sébastien Hinderer and Miod Vallat)

[avsm]

Thanks!