[sledge] Suppress warning on dune build_info compilation

Summary:
Previously building would spew:
```
Warning 58: no cmx file was found in path for module Build_info__Build_info_data, and its interface was not compiled with -opaque
```
This is from compilation of the generated `build_info_data.ml-gen`. It
does not have an interface, so I don't how to resolve this other than
disabling the warning.

See also https://github.com/ocaml/dune/issues/3277 .

Reviewed By: jvillard

Differential Revision: D20589879

fbshipit-source-id: fcd86fb3b

sledge/bin/dune

@@ -11,6 +11,6 @@
    llvm.irreader llvm.analysis llvm.scalar_opts llvm.target llvm.ipo
    llvm.linker shexp.process yojson trace import sledge model)
  (flags
-  (:standard -open Import -open Sledge -open Model))
+  (:standard -w -58 -open Import -open Sledge -open Model))
  (preprocess
   (pps ppx_sledge)))