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)"; }; \
26c633a0ee88fe7a81'>tree</a><a href='/guix/commit/doc/fdl-1.3.texi?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81'>commit</a><a href='/guix/diff/doc/fdl-1.3.texi?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/doc/fdl-1.3.texi'>
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<div class='path'>path: <a href='/guix/log/?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81'>root</a>/<a href='/guix/log/doc?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81'>doc</a>/<a href='/guix/log/doc/fdl-1.3.texi?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81'>fdl-1.3.texi</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/doc/fdl-1.3.texi?id=cad1789b3ea7317fd41a6a26c633a0ee88fe7a81&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
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<tr><td><span title='2020-03-23 00:06:58 +0100'>2020-03-23</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=8b18f5cb309f670b08ad35df6425f4e9e19d8a82'>tests: Use the same source as ci.guix.gnu.org.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/system-tests.scm (system-test-manifest): In 'local-file' call, use
a name that is a function of COMMIT to match what Cuirass does.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 16:33:38 +0100'>2020-03-05</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=5ec4156bbcaec8337f78411204d59e59e706103b'>tests: Add a manifest for system tests.</a><span class='msg-avail'>...<span class='msg-tooltip'>The manifest can be passed to 'guix build -m', 'guix weather -m', and so
on.  It can also be passed to an installed 'guix' (without
./pre-inst-env), with the exception so far of installation tests.

* build-aux/run-system-tests.scm: Remove.  Move interesting bits move
to...
* etc/system-tests.scm: ... here.  New file.
* Makefile.am (EXTRA_DIST): Remove 'build-aux/run-system-tests.scm' and
add 'etc/system-tests.scm'.
(check-system): Rewrite to run 'guix build -m etc/system-tests.scm'.
</span></span></td><td>Ludovic Courtès</td></tr>