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)"; }; \
in?id=e82c98abe93c749296c831691c7c67c736f0807f'>tree</a><a href='/guix/commit/po/packages/POTFILES.in?id=e82c98abe93c749296c831691c7c67c736f0807f'>commit</a><a href='/guix/diff/po/packages/POTFILES.in?id=e82c98abe93c749296c831691c7c67c736f0807f'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/po/packages/POTFILES.in'>
<input type='hidden' name='id' value='e82c98abe93c749296c831691c7c67c736f0807f'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=e82c98abe93c749296c831691c7c67c736f0807f'>root</a>/<a href='/guix/log/po?id=e82c98abe93c749296c831691c7c67c736f0807f'>po</a>/<a href='/guix/log/po/packages?id=e82c98abe93c749296c831691c7c67c736f0807f'>packages</a>/<a href='/guix/log/po/packages/POTFILES.in?id=e82c98abe93c749296c831691c7c67c736f0807f'>POTFILES.in</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/po/packages/POTFILES.in?id=e82c98abe93c749296c831691c7c67c736f0807f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-11-28 23:34:25 +0100'>2017-11-28</span></td><td><a href='/guix/commit/po/packages/POTFILES.in?id=3af03e5967cf49ed1a4382dad7d75daa95ec5217'>services: certbot: Add default value and description.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-28 23:34:25 +0100'>2017-11-28</span></td><td><a href='/guix/commit/po/packages/POTFILES.in?id=a222b734b38f93b014b21e4d538002a5fec71b8a'>services: cgit, git-daemon: Add description and default value.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-09-16 17:47:46 +0200'>2017-09-16</span></td><td><a href='/guix/commit/po/packages/POTFILES.in?id=3f0de257c4071fcbb167fd47dbe6ffa71e95631a'>services: networking: Add descriptions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-09-16 17:47:46 +0200'>2017-09-16</span></td><td><a href='/guix/commit/po/packages/POTFILES.in?id=6b9e1fefa40ecdd264fde9cb022b2b5359635ee5'>services: base: Add descriptions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-07-15 19:25:39 +0800'>2017-07-15</span></td><td><a href='/guix/commit/po/packages/POTFILES.in?id=ee38fbcfaa5afc1cf2bb121a04bc9747b2339c37'>nls: Adjust to qemu.scm renaming.</a><span class='msg-avail'>...</span></td><td>宋文武</td></tr>