dev-ml/topkg: fix build without ocamlopt

Closes: https://bugs.gentoo.org/795987
Signed-off-by: Sam James <sam@gentoo.org>

dev-ml/topkg/topkg-1.0.3.ebuild

@@ -12,12 +12,12 @@ SRC_URI="https://github.com/dbuenzli/topkg/archive/v${PV}.tar.gz -> ${P}.tar.gz"
 LICENSE="ISC"
 SLOT="0/${PV}"
 KEYWORDS="amd64 arm arm64 ppc ppc64 x86"
-IUSE=""
+IUSE="+ocamlopt"
 
 RDEPEND="dev-ml/result:=
 	dev-ml/ocamlbuild:=
 	dev-ml/findlib:=
-	dev-lang/ocaml:="
+	dev-lang/ocaml:=[ocamlopt?]"
 DEPEND="${RDEPEND}"
 
 src_compile() {
@@ -27,7 +27,12 @@ src_compile() {
 src_install() {
 	# Can't use opam-installer here as it is an opam dep...
 	findlib_src_preinst
-	local nativelibs="$(echo _build/src/${PN}*.cm{x,xa,xs,ti} _build/src/${PN}.a)"
+
+	local nativelibs
+	if use ocamlopt; then
+		nativelibs=$(echo _build/src/${PN}*.cm{x,xa,xs,ti} _build/src/${PN}.a)
+	fi
+
 	ocamlfind install ${PN} _build/pkg/META _build/src/${PN}.mli _build/src/${PN}.cm{a,i} ${nativelibs} || die
 	dodoc CHANGES.md DEVEL.md README.md
 }