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)"; }; \
/wxwidgets.scm?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>tree</a><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>commit</a><a href='/guix/diff/gnu/packages/wxwidgets.scm?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/wxwidgets.scm'>
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<div class='path'>path: <a href='/guix/log/?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>root</a>/<a href='/guix/log/gnu?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>gnu</a>/<a href='/guix/log/gnu/packages?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>packages</a>/<a href='/guix/log/gnu/packages/wxwidgets.scm?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f'>wxwidgets.scm</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/gnu/packages/wxwidgets.scm?id=0b469ee225b9a043a68302e6d78f2ddac1b84c6f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-01-07 14:41:00 +0100'>2019-01-07</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=6fd5a80dbe7013fc37aa1228051d02b42ee76527'>gnu: Remove unnecessary build-side module imports.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-11-29 22:43:48 +0100'>2018-11-29</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=3962a0469710811f5f9b211772c73cdd8743b60d'>gnu: wxwidgets-3.1: Fetch sources from git.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2018-09-21 19:52:26 +0200'>2018-09-21</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=9a32bdf8a9b56eec84310a809820eadd1a33f45f'>gnu: wxwidgets: Update to 3.0.4.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-03-16 09:08:31 -0400'>2018-03-16</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=6cbee49d6668eb7fd738080666f66febfce8c7e8'>gnu: All snippets report errors using exceptions, else return #t.</a><span class='msg-avail'>...</span></td><td>Mark H Weaver</td></tr>
<tr><td><span title='2018-02-22 14:35:51 +0100'>2018-02-22</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=1aef4222b6e1b27ab0f125a012c75a23f6523aaa'>Revert "gnu: Remove wxwidgets@2.8."</a><span class='msg-avail'>...</span></td><td>Björn Höfling</td></tr>
<tr><td><span title='2018-02-22 09:07:25 +0100'>2018-02-22</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=3fd2ecb338ed1224dc5df6ac4359365e6b1bc082'>gnu: Add wxwidgets-gtk2-3.1.</a><span class='msg-avail'>...</span></td><td>David Thompson</td></tr>
<tr><td><span title='2018-01-23 01:06:18 +0100'>2018-01-23</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=afb7cd8e667bdf2c814e5c7ffe4cc663b3a4b8ec'>Revert "gnu: wxwidgets: Use webkitgtk-2.4."</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2018-01-22 19:51:50 +0100'>2018-01-22</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=8a58182c12193ae27359591c92febfdd602411f4'>gnu: wxwidgets: Use webkitgtk-2.4.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2018-01-20 22:27:34 +0100'>2018-01-20</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=e81c906647b64c69d116f3558321cf2a85eb8a13'>gnu: wxsvg: Update to 1.5.12.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-10-03 17:07:54 +0200'>2017-10-03</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=d109b1e85c5c1438e66dfc05ea4a018418edaf19'>Update e-mail for Theodoros Foradis.</a><span class='msg-avail'>...</span></td><td>Theodoros Foradis</td></tr>
<tr><td><span title='2017-08-27 16:04:25 -0400'>2017-08-27</span></td><td><a href='/guix/commit/gnu/packages/wxwidgets.scm?id=1c059a6e1635ef3f52982ae0470f53b7693feae8'>gnu: wxwidgets: Update to 3.0.3.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>