message: make which crate optional too
diff: @@ -32,7 +32,7 @@ once_cell = "1.0"
  rayon = "1.0"
  regex = "1.0"
  semver = "0.9"
  -which_crate = {package = "which", version = "3.0", default-features = false}
  +which_crate = {package = "which", version = "3.0", optional = true, default-features = false}
  [target.'cfg(not(target_env = "msvc"))'.build-dependencies]
  pkg-config = "0.3"
  @@ -45,7 +45,7 @@ matches = "0.1"
  [features]
  default = ["opencv-34"]
  -buildtime-bindgen = []
  +buildtime-bindgen = ["which_crate"]
  force-3rd-party-libs-discovery = []
  opencv-32 = []
  opencv-34 = []
  