Log message:
ocaml-lablgtk3: update to 3.1.5.

## In Lablgtk-3.1.5

2024.06.10 [Jacques]
  * Prepare for release
  * Fix typos in README.md (#182) [Sylvain Chiron]

2024.05.20 [Jacques]
  * Typo in ml_gtk_text_buffer_get_iter_at_line_index. (#181) [Hugo Herbelin]

2024.05.14 [Jacques]
  * Support windows sockets in Glib.IO.channel_of_descr (#176)
    [with Michael Soegtrop]

2024.03.24 [Jacques]
  * fix pointer incompatibility in ml_gtk_style_context_list_classes (#178)

## In Lablgtk-3.1.4

2024.01.31 [Jacques]
  * use Bytes rather than String
  * Various missing bindings, including lablgtk3-rsvg2 (#128)
  * GtkStyleContext: Add missing class and provider functions (#163)
  * Add GdkEvent.Scroll.delta_{x,y} (#173) [Thomas Leonard]

Log message:
*: recursive bump for pango requiring fontconfig 2.15

Log message:
x11/ocaml-lablgtk3: Remove dune/PKGCONFIG kludge

as no longer necessary/useful now that the bug is patched in dune and
the patch is actually used in the build.

No PKGREVISION++; this is just swapping a dune fix for a dune
workaround, with no expected change in the binary.

Log message:
x11/ocaml-lablgtk3: Add comment about perhaps-similar pkg-config-finding problem

Log message:
x11/ocaml-lablgtk3: Improve kludge comments

NFCI

Log message:
x11/ocaml-lablgtk3: Kludge around dune pkg-config issues

For unclear reasons, if PKG_CONFIG is set in the environment, even if
properly to a copy of pkg-config in the work directory, dune objects
to it and errors out.  Remove PKG_CONFIG from the build environment.
This allows building to succeed.

This commit adds some test targets, not invoked, with comments that
are notes to the next person struggling with this, perhaps future
self.

The removal of PKG_CONFIG is implemented by open-coding the do-build
target from ocaml.mk, pending disscussion of the wisdom of changing
that target, on the theory that this is a dune bug, not a lablgtk bug.

Log message:
x11/ocaml-lablgtk3: Add -verbose when using pkg-config

This doesn't fix the build, but it provides a clue: dune code is
objecting to the pkg-config that is found, which is a shell script
wrapper:

  File "src/dune", line 9, characters 0-128:
   9 | (rule
  10 |  (targets
  11 |    cflag-gtk+-3.0.sexp
  12 |    clink-gtk+-3.0.sexp)
  13 |  (action (run dune_config -verbose -pkg gtk+-3.0 -version 3.18)))
  (cd _build/default/src && ../.bin/dune_config -verbose -pkg gtk+-3.0 \ 
-version 3.18)
  which: /tmp/work/x11/ocaml-lablgtk3/work/.tools/bin/pkg-config
  -> not found
  configure error: pkg_config not installed

Take maintainership (offlist discussion with jaapb@).

Log message:
*: recursive bump for default-on option of at-spi2-core