Ocaml wants to install its "core" libraries in OCAML_CORE_STDLIB.  That
does not work in a store-based distribution.

A solution was already provided by Nix

    https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/ocaml/findlib/install_topfind.patch

regenerated for Guix.

--- findlib-1.5.3/src/findlib/Makefile	2014-09-16 13:21:46.000000000 +0200
+++ findlib-1.5.3/src/findlib/Makefile.new	2014-10-01 14:30:54.141082521 +0200
@@ -89,7 +89,7 @@
 install: all
 	mkdir -p "$(prefix)$(OCAML_SITELIB)/$(NAME)"
 	mkdir -p "$(prefix)$(OCAMLFIND_BIN)"
-	test $(INSTALL_TOPFIND) -eq 0 || cp topfind "$(prefix)$(OCAML_CORE_STDLIB)"
+	test $(INSTALL_TOPFIND) -eq 0 || cp topfind "$(prefix)$(OCAML_SITELIB)"
 	files=`$(TOP)/tools/collect_files $(TOP)/Makefile.config findlib.cmi findlib.mli findlib.cma topfind.cmi topfind.mli fl_package_base.mli fl_package_base.cmi fl_metascanner.mli fl_metascanner.cmi fl_metatoken.cmi findlib_top.cma findlib.cmxa findlib.a findlib.cmxs findlib_dynload.cma findlib_dynload.cmxa findlib_dynload.a findlib_dynload.cmxs fl_dynload.mli fl_dynload.cmi META` && \
 	cp $$files "$(prefix)$(OCAML_SITELIB)/$(NAME)"
 	f="ocamlfind$(EXEC_SUFFIX)"; { test -f ocamlfind_opt$(EXEC_SUFFIX) && f="ocamlfind_opt$(EXEC_SUFFIX)"; }; \
t/NEWS?id=ee394937bc1ccac3a1d68e654cb7904b2b66e972'>commit</a><a href='/guix/diff/NEWS?id=ee394937bc1ccac3a1d68e654cb7904b2b66e972'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/NEWS'>
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</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=ee394937bc1ccac3a1d68e654cb7904b2b66e972'>root</a>/<a href='/guix/log/NEWS?id=ee394937bc1ccac3a1d68e654cb7904b2b66e972'>NEWS</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/NEWS?id=ee394937bc1ccac3a1d68e654cb7904b2b66e972&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-09-23 20:02:23 +0200'>2021-09-23</span></td><td><a href='/guix/commit/NEWS?id=ff775440218c4f576d51aa01ce419b1fb786170a'>Update NEWS.</a><span class='msg-avail'>...<span class='msg-tooltip'>* NEWS (Distribution): Note new fsck.* arguments and XFS support.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-09-18 23:08:32 +0200'>2021-09-18</span></td><td><a href='/guix/commit/NEWS?id=eb6593cec4b0cedef44bf156e2e6727ead82006c'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-07-07 23:54:20 -0400'>2021-07-07</span></td><td><a href='/guix/commit/NEWS?id=4cbe0127a668cbcc64087c5d311308b59d39b104'>guix-install.sh: Prompt for configuring substitutes discovery.</a><span class='msg-avail'>...<span class='msg-tooltip'>Also ensure prompt_yes_no always print the message with a trailing space,
which is more pleasing to the eye.

* etc/guix-daemon.conf.in &lt;--discover=no&gt;: New guix-daemon option.
* etc/guix-daemon.service.in: Likewise.
* etc/init.d/guix-daemon.in: Likewise.
* etc/openrc/guix-daemon.in: Likewise.
* etc/guix-install.sh (configure_substitute_discovery): New procedure.
(sys_enable_guix_daemon): Ask the user whether automatic substitute discovery
should be enabled.  Set the '--discover' argument accordingly.
(prompt_yes_no): Add a trailing space to the message.
(sys_authorize_build_farms): Remove trailing space from the message argument.
* NEWS (Distribution): Add news.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-06-29 14:53:21 -0400'>2021-06-29</span></td><td><a href='/guix/commit/NEWS?id=82daab42811a2e3c7684ebdf12af75ff0fa67b99'>pack: Add support for the deb format.</a><span class='msg-avail'>...<span class='msg-tooltip'>* .dir-locals.el (scheme-mode)[gexp-&gt;derivation]: Define indentation rule.
* guix/scripts/pack.scm (debian-archive): New procedure.
(%formats): Register the new deb format.
(show-formats): Add it to the usage string.
* tests/pack.scm (%ar-bootstrap): New variable.
(deb archive with symlinks): New test.
* doc/guix.texi (Invoking guix pack): Document it.
* NEWS: Add news entry.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-05-10 13:48:30 -0400'>2021-05-10</span></td><td><a href='/guix/commit/NEWS?id=80dc6ad4a89b68b5e837fc22c9b1322b86527bef'>Update NEWS.</a></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-05-10 11:21:02 -0400'>2021-05-10</span></td><td><a href='/guix/commit/NEWS?id=7418a200742768d21b567916b25e4d3351472230'>Update NEWS.</a></td><td>Leo Famulari</td></tr>
<tr><td><span title='2021-05-10 11:42:03 +0200'>2021-05-10</span></td><td><a href='/guix/commit/NEWS?id=3a0fcaa0fe721792d1543e863c3fba805376bdac'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-05-04 16:57:05 +0200'>2021-05-04</span></td><td><a href='/guix/commit/NEWS?id=b37ab28401c55adbb8e36ea2931849636752524d'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-22 20:27:28 +0100'>2020-11-22</span></td><td><a href='/guix/commit/NEWS?id=a099685659b4bfa6b3218f84953cbb7ff9e88063'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-13 09:13:56 +0100'>2020-11-13</span></td><td><a href='/guix/commit/NEWS?id=1e272d42f6217b70c9801b93e46b144e9ab27664'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-09 23:27:09 +0100'>2020-11-09</span></td><td><a href='/guix/commit/NEWS?id=b51da3ccef74e5842b87e39eea839e36831e844e'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-07 19:36:10 +0100'>2020-11-07</span></td><td><a href='/guix/commit/NEWS?id=afa77bd2287f303aefdd00193309ccf57f6dcd93'>Update NEWS.</a></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-11-07 16:14:03 +0100'>2020-11-07</span></td><td><a href='/guix/commit/NEWS?id=e8b9b0fae076a86e2be1dcb87b666d4490bac0aa'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-05 23:27:22 +0100'>2020-11-05</span></td><td><a href='/guix/commit/NEWS?id=51916455d0bb283489162ef84afc8145b28b012c'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-04-15 00:02:23 +0200'>2020-04-15</span></td><td><a href='/guix/commit/NEWS?id=d62c9b2671be55ae0305bebfda17b595f33797f2'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-04-12 17:05:21 +0200'>2020-04-12</span></td><td><a href='/guix/commit/NEWS?id=6945c43754308f64ad177fd29fa515959243f155'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-04-09 22:56:56 +0200'>2020-04-09</span></td><td><a href='/guix/commit/NEWS?id=f9adf3559543bdbcecad45280c9c626b63e84e95'>Update NEWS.</a></td><td>Ludovic Courtès</td></tr>