Define have_ocaml macro.

Use it in place of %{ocaml_native_compiler}.

Use --disable-ocaml on non-OCaml platforms.

Make the example.ml file conditional.

nbdkit.spec

@@ -4,6 +4,12 @@
 %global have_libguestfs 1
 %endif
 
+# We can only compiler the OCaml plugin on platforms which have native
+# OCaml support (not bytecode).
+%ifarch %{ocaml_native_compiler}
+%global have_ocaml 1
+%endif
+
 # Architectures where the complete test suite must pass.
 #
 # On all other architectures, a simpler test suite must pass.  This
@@ -72,7 +78,7 @@ BuildRequires:  bash-completion
 BuildRequires:  perl-devel
 BuildRequires:  perl(ExtUtils::Embed)
 BuildRequires:  python3-devel
-%ifarch %{ocaml_native_compiler}
+%if 0%{?have_ocaml}
 # Requires OCaml 4.02.2 which contains fix for
 # http://caml.inria.fr/mantis/view.php?id=6693
 BuildRequires:  ocaml >= 4.02.2
@@ -316,7 +322,7 @@ This package lets you forward NBD connections from %{name}
 to another NBD server.
 
 
-%ifarch %{ocaml_native_compiler}
+%if 0%{?have_ocaml}
 %package ocaml-plugin
 Summary:        OCaml plugin for %{name}
 License:        BSD
@@ -564,6 +570,11 @@ autoreconf -i
 %configure \
     PYTHON=%{_bindir}/python3 \
     --disable-static \
+%if 0%{?have_ocaml}
+    --enable-ocaml \
+%else
+    --disable-ocaml \
+%endif
 %if 0%{?have_libguestfs}
     --with-libguestfs \
 %else
@@ -613,7 +624,7 @@ make %{?_smp_mflags} check || {
   }
 
 
-%ifarch %{ocaml_native_compiler}
+%if 0%{?have_ocaml}
 %ldconfig_scriptlets plugin-ocaml
 %endif
 
@@ -745,7 +756,7 @@ make %{?_smp_mflags} check || {
 %{_mandir}/man1/nbdkit-nbd-plugin.1*
 
 
-%ifarch %{ocaml_native_compiler}
+%if 0%{?have_ocaml}
 %files ocaml-plugin
 %doc README
 %license LICENSE
@@ -866,7 +877,9 @@ make %{?_smp_mflags} check || {
 %doc plugins/example*/*.c
 %doc plugins/example4/nbdkit-example4-plugin
 %doc plugins/lua/example.lua
+%if 0%{?have_ocaml}
 %doc plugins/ocaml/example.ml
+%endif
 %doc plugins/perl/example.pl
 %doc plugins/python/example.py
 %doc plugins/ruby/example.rb