Make lwt subpackage conditional.

This breaks a circular dependency between ocaml-ounit <-> ocaml-lwt.

Intend to reenable this later to complete the OCaml 4.10.0 build.

ocaml-ounit.spec

@@ -4,6 +4,8 @@
 
 %global srcname ounit
 
+%bcond_with lwt
+
 Name:           ocaml-%{srcname}
 Version:        2.2.2
 Release:        2%{?dist}
@@ -20,7 +22,9 @@ Patch0:         %{name}-stdlib-shims.patch
 BuildRequires:  ocaml >= 4.02.3
 BuildRequires:  ocaml-dune >= 1.11.0
 BuildRequires:  ocaml-findlib
+%if %{with lwt}
 BuildRequires:  ocaml-lwt-devel
+%endif
 BuildRequires:  ocaml-mmap-devel
 BuildRequires:  ocaml-ocplib-endian-devel
 BuildRequires:  ocaml-odoc
@@ -47,6 +51,7 @@ The %{name}-devel package contains libraries and signature files for
 developing applications that use %{name}.
 
 
+%if %{with lwt}
 %package        lwt
 Summary:        Helper functions for building Lwt tests using OUnit
 Requires:       %{name} = %{version}-%{release}
@@ -69,6 +74,7 @@ Provides:       %{name}2-lwt-devel = %{version}-%{release}
 %description    lwt-devel
 The %{name}-lwt-devel package contains libraries and signature
 files for developing applications that use %{name}-lwt.
+%endif
 
 
 %package        doc
@@ -151,6 +157,7 @@ find %{buildroot}%{_libdir}/ocaml -name \*.cmxs -exec chmod a+x {} \+
 %{_libdir}/ocaml/%{srcname}2/*/*.mli
 
 
+%if %{with lwt}
 %files lwt
 %dir %{_libdir}/ocaml/%{srcname}-lwt/
 %dir %{_libdir}/ocaml/%{srcname}2-lwt/
@@ -175,6 +182,7 @@ find %{buildroot}%{_libdir}/ocaml -name \*.cmxs -exec chmod a+x {} \+
 %endif
 %{_libdir}/ocaml/%{srcname}2-lwt/oUnitLwt.cmt
 %{_libdir}/ocaml/%{srcname}2-lwt/oUnitLwt.ml
+%endif
 
 
 %files doc
@@ -187,6 +195,7 @@ find %{buildroot}%{_libdir}/ocaml -name \*.cmxs -exec chmod a+x {} \+
 %changelog
 * Wed Feb 26 2020 Richard W.M. Jones <rjones@redhat.com> - 2.2.2-2
 - OCaml 4.10.0 final.
+- Make lwt subpackage conditional.
 
 * Fri Feb  7 2020 Jerry James <loganjerry@gmail.com> - 2.2.2-1
 - New upstream version 2.2.2