Add BR libev-devel, see comment for why.

ocaml-ounit.spec

@@ -33,6 +33,12 @@ BuildRequires:  ocaml-odoc
 %endif
 BuildRequires:  ocaml-result-devel
 
+# I believe this is actually caused by a missing Requires in another
+# package (perhaps lwt?).  In any case without this the tests fail to
+# compile with:
+# /usr/bin/ld: cannot find -lev
+BuildRequires:  libev-devel
+
 # The ounit name is now just an alias for ounit2
 Provides:       %{name}2 = %{version}-%{release}