[sledge] Suppress newly flagged no-cmx-file warning

Summary:
These no-cmx-file warnings on libraries in dependencies do not seem to
be resolvable, and there is no smaller scope I can find to suppress
them.

Reviewed By: jvillard

Differential Revision: D27280739

fbshipit-source-id: 6e8886f7f

sledge/nonstdlib/dune

@@ -7,7 +7,7 @@
  (name NS)
  (public_name nonstdlib)
  (libraries containers containers-data core_kernel.fheap iter zarith trace)
- (flags (:standard))
+ (flags (:standard -w -no-cmx-file))
  (preprocess
   (pps ppx_sledge ppx_trace))
  (inline_tests))