put benchmark compilation into oasis

Makefile

@@ -40,12 +40,6 @@ configure:
 
 # OASIS_STOP
 
-benchs: all
-	ocamlbuild -use-ocamlfind -pkg benchmark -pkg unix \
-		bench/benchs.native bench/simple_bench.native \
-		bench/bench_persistent.native \
-		bench/bench_persistent_read.native
-
 tests:
 	ocamlbuild -use-ocamlfind -pkg oUnit tests/run_tests.native
 

_oasis

@@ -15,6 +15,10 @@ Description:
     like `filter`, `map`, `take`, `drop` and `append` can be performed before the
     sequence is iterated/folded on.
 
+Flag bench
+    Description: enable benchmarks (require library Benchmark)
+    Default: false
+
 Library "sequence"
   Path:             .
   Modules:          Sequence 
@@ -31,6 +35,30 @@ Test all
   Type:         custom
   Command:      make tests
 
+Executable benchs
+  Path:             bench
+  Install:          false
+  CompiledObject:   native
+  Build$:           flag(bench)
+  BuildDepends:     sequence,benchmark
+  MainIs:           benchs.ml
+
+Executable bench_persistent
+  Path:             bench
+  Install:          false
+  CompiledObject:   native
+  Build$:           flag(bench)
+  BuildDepends:     sequence,benchmark
+  MainIs:           bench_persistent.ml
+
+Executable bench_persistent_read
+  Path:             bench
+  Install:          false
+  CompiledObject:   native
+  Build$:           flag(bench)
+  BuildDepends:     sequence,benchmark
+  MainIs:           bench_persistent_read.ml
+
 SourceRepository head
   Type: git
   Location: https://github.com/c-cube/sequence