build: create group features for target systems

This allows a user to create builds with or without the Unix-specific
utilities. Right now the Makefile handles this, but this is needed to
migrate away from make.

To build Unix-specific utilities (default):

cargo build
(or)
cargo build --features unix --no-default-features

To build without the Unix-specific utilities:

cargo build --features generic --no-default-features

Cargo.toml

@@ -4,85 +4,86 @@ version = "0.0.1"
 authors = []
 build = "build.rs"
 
-
 [features]
-default = ["all"]
-all = [
-    "base64",
-    "basename",
-    "cat",
-    "chmod",
-    "chroot",
-    "cksum",
-    "comm",
-    "cp",
-    "cut",
-    "dirname",
-    "du",
-    "echo",
-    "env",
-    "expand",
-    "expr",
-    "factor",
-    "false",
-    "fmt",
-    "fold",
-    "groups",
-    "hashsum",
-    "head",
-    "hostid",
-    "hostname",
-    "id",
-    "kill",
-    "link",
-    "ln",
-    "logname",
-    "mkdir",
-    "mkfifo",
-    "mv",
-    "nice",
-    "nl",
-    "nohup",
-    "nproc",
-    "od",
-    "paste",
-    "printenv",
-    "ptx",
-    "pwd",
-    "readlink",
-    "realpath",
-    "relpath",
-    "rm",
-    "rmdir",
-    "seq",
-    "shuf",
-    "sleep",
-    "sort",
-    "split",
-    "stdbuf",
-    "sum",
-    "sync",
-    "tac",
-    "tail",
-    "tee",
-    "test",
-    "timeout",
-    "touch",
-    "tr",
-    "true",
-    "truncate",
-    "tsort",
-    "tty",
-    "uname",
-    "unexpand",
-    "uniq",
-    "unlink",
-    "uptime",
-    "users",
-    "wc",
-    "whoami",
-    "yes",
+unix = [
+  "chroot",
+  "du",
+  "groups",
+  "hostid",
+  "hostname",
+  "id",
+  "kill",
+  "logname",
+  "mkfifo",
+  "mv",
+  "nice",
+  "nohup",
+  "stdbuf",
+  "timeout",
+  "touch",
+  "tty",
+  "uname",
+  "unlink",
+  "uptime",
+  "users",
 ]
+generic = [
+  "base64",
+  "basename",
+  "cat",
+  "chmod",
+  "cksum",
+  "comm",
+  "cp",
+  "cut",
+  "dirname",
+  "echo",
+  "env",
+  "expand",
+  "expr",
+  "factor",
+  "false",
+  "fmt",
+  "fold",
+  "hashsum",
+  "head",
+  "link",
+  "ln",
+  "mkdir",
+  "nl",
+  "nproc",
+  "od",
+  "paste",
+  "printenv",
+  "ptx",
+  "pwd",
+  "readlink",
+  "realpath",
+  "relpath",
+  "rm",
+  "rmdir",
+  "seq",
+  "shuf",
+  "sleep",
+  "sort",
+  "split",
+  "sum",
+  "sync",
+  "tac",
+  "tail",
+  "tee",
+  "test",
+  "tr",
+  "true",
+  "truncate",
+  "tsort",
+  "unexpand",
+  "uniq",
+  "wc",
+  "whoami",
+  "yes",
+]
+default = ["generic", "unix"]
 
 [dependencies]
 uucore   = { path="src/uucore" }
@@ -178,4 +179,3 @@ tempdir="*"
 [[bin]]
 name="uutils"
 path="src/uutils/uutils.rs"
-