Provide for linking the native toplevel now exposed as 'ocamltoplevel.cmxa'

[AltGr]

See ocaml/ocaml#10124

This is clearly not optimal, since it will force linking to the native
backend and dynlink even for bytecode mode ; is there a way to specify
requires(byte) and requires(native) ?

[AltGr]

An alternative which may be better is to provide it as an alternate package:

modified   site-lib-src/compiler-libs/META.in
@@ -30,10 +30,16 @@
 `)'
 
 `package "toplevel" ('
-`  requires = "compiler-libs.bytecomp compiler-libs.optcomp dynlink"'
+`  requires = "compiler-libs.bytecomp"'
 `  version = "[distributed with Ocaml]"'
 `  description = "Toplevel interactions"'
 `  archive(byte) = "ocamltoplevel.cma"'
+`)'
+
+`package "native-toplevel" ('
+`  requires = "compiler-libs.bytecomp compiler-libs.optcomp dynlink"'
+`  version = "[distributed with Ocaml]"'
+`  description = "Toplevel interactions"'
 `  archive(native) = "ocamltoplevel.cmxa"'
 `)'

So consumers of the current toplevel won't see a change of behaviour, and it's easy to switch to try a native build.

[gerdstolpmann]

@AltGr unfortunately there is no requires(byte) and requires(native) (only one deps tree), so I think the separate package is the better way to go.

[emillon]

I'm not sure how versioning works in ocamlfind, but does this change in the installed META file happen for all compiler versions?

[gerdstolpmann]

@emillon if the META files have to be different by compiler version, the only way is to check the version in the configure script and generate the META file from that.

[AltGr]

Updated with the separate version, where I added an exists_if so that it shouldn't need modifying depending on the OCaml version.

[ghost]

@gerdstolpmann does the current state of the PR looks good to you? The corresponding changes to OCaml have now been merged.

[gerdstolpmann]

Looks good