Preventive compatibility fixes for flushing.

In pre 8.6, `Pp` provided its own reimplementation of
`Pervasives.flush_all`, with different semantics.

Unfortunately, with the removal of `Pp.flush_all` in #179, a couple of
points were silently switched to the `Pervasives` version, which may
lead to some subtle printing differences.

As a preventive measure, we restore the same semantics for these parts
of the codebase.

Note that we don't re-introduce Coq's `flush_all` for several reasons:

- Consumers of the logging API should not mess with flushing and
  Formatters as this is backend dependent (i.e: when in IDEs).

  Use of `Format` should be fully encapsulated if we want some hope of
  IDEs taking full control.

- As used, the old semantics of `flush_all` were fragile.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/errors.ml b/lib/errors.ml
index 8982dde14..1459141d1 100644
--- a/lib/errors.ml
+++ b/lib/errors.ml
@@ -144,5 +144,5 @@ let handled e =
 let fatal_error info anomaly =
   let msg = info ++ fnl () in
   pp_with ~pp_tag:Ppstyle.pp_tag !Pp_control.err_ft msg;
-  flush_all ();
+  Format.pp_print_flush !Pp_control.err_ft ();
   exit (if anomaly then 129 else 1)