[sledge] Dedup preprocess entries in dune files

Summary:
Define a `ppx_sledge` ppx rewriter that composes all the ppx rewriters
used, so that the list needs to be specified only once.

Reviewed By: jvillard

Differential Revision: D20322874

fbshipit-source-id: f15540b7f

sledge/bin/dune

@@ -12,5 +12,4 @@
  (flags
   (:standard -open Import -open Sledgelib -open Model))
  (preprocess
-  (pps ppx_compare ppx_custom_printf ppx_expect ppx_hash ppx_here
-    ppx_inline_test ppx_let ppx_sexp_conv ppx_sexp_value ppx_trace)))
+  (pps ppx_sledge)))

sledge/lib/dune

@@ -9,6 +9,5 @@
  (flags
   (:standard -open Import))
  (preprocess
-  (pps ppx_compare ppx_custom_printf ppx_expect ppx_hash ppx_here
-    ppx_inline_test ppx_let ppx_sexp_conv ppx_sexp_value ppx_trace))
+  (pps ppx_sledge))
  (inline_tests))

sledge/lib/import/dune

@@ -9,6 +9,5 @@
  (libraries core core_kernel.fheap zarith trace)
  (flags (:standard))
  (preprocess
-  (pps ppx_compare ppx_custom_printf ppx_expect ppx_hash ppx_here
-    ppx_inline_test ppx_let ppx_sexp_conv ppx_sexp_value ppx_trace))
+  (pps ppx_sledge))
  (inline_tests))

sledge/ppx_sledge/dune

@@ -0,0 +1,11 @@
+; Copyright (c) Facebook, Inc. and its affiliates.
+;
+; This source code is licensed under the MIT license found in the
+; LICENSE file in the root directory of this source tree.
+
+(library
+ (name ppx_sledge)
+ (kind ppx_rewriter)
+ (libraries ppx_compare ppx_custom_printf ppx_expect ppx_hash ppx_here
+   ppx_inline_test ppx_let ppx_sexp_conv ppx_sexp_value ppx_trace)
+ (preprocess no_preprocessing))