Wrap more deps behind installer feature

Cargo.toml

@@ -28,7 +28,7 @@ arg_parser = "0.1.0"
 fatfs = { version = "0.3.0", optional = true }
 fscommon = { version = "0.1.1", optional = true }
 gpt = { version = "3.0.0", optional = true }
-libc = "0.2.70"
+libc = { version = "0.2.70", optional = true }
 pkgar = { version = "0.2", optional = true }
 pkgar-core = { version = "0.2", optional = true }
 pkgar-keys = { version = "0.2", optional = true }
@@ -44,8 +44,8 @@ toml = "0.8"
 uuid = { version = "1.4", features = ["v4"], optional = true }
 
 [target.'cfg(target_os = "redox")'.dependencies]
-libredox = "0.1"
-ring = "=0.17.8"
+libredox = { version = "0.1", optional = true }
+ring = { version = "=0.17.8", optional = true }
 
 [features]
 default = ["installer", "fuse"]
@@ -53,6 +53,8 @@ installer = [
     "fatfs",
     "fscommon",
     "gpt",
+    "libc",
+    "libredox",
     "pkgar",
     "pkgar-core",
     "pkgar-keys",
@@ -60,6 +62,7 @@ installer = [
     "redox-pkg",
     "redox_syscall",
     "redoxfs",
+    "ring",
     "rust-argon2",
     "termion",
     "uuid",