Move os.system from posix.rs to os.rs

Fixes RustPython#5100

Author: oskar-skog

extra_tests/snippets/stdlib_os.py

@@ -502,9 +502,9 @@ def __exit__(self, exc_type, exc_val, exc_tb):
             assert set(collected_files) == set(expected_files)
 
 # system()
-if "win" not in sys.platform:
-    assert os.system('ls') == 0
-    assert os.system('{') != 0
+if os.name in ('posix', 'nt'):
+    assert os.system('echo test') == 0
+    assert os.system('&') != 0
 
     for arg in [None, 1, 1.0, TabError]:
         assert_raises(TypeError, os.system, arg)

vm/src/stdlib/os.rs

@@ -142,6 +142,7 @@ pub(super) mod _os {
         protocol::PyIterReturn,
         recursion::ReprGuard,
         types::{IterNext, Iterable, PyStructSequence, Representable, SelfIter},
+        utils::ToCString,
         vm::VirtualMachine,
         AsObject, Py, PyObjectRef, PyPayload, PyRef, PyResult, TryFromObject,
     };
@@ -1028,6 +1029,14 @@ pub(super) mod _os {
         })
     }
 
+    #[cfg(any(unix, windows))]
+    #[pyfunction]
+    fn system(command: PyStrRef, vm: &VirtualMachine) -> PyResult<i32> {
+        let cstr = command.to_cstring(vm)?;
+        let x = unsafe { libc::system(cstr.as_ptr()) };
+        Ok(x)
+    }
+
     #[derive(FromArgs)]
     struct UtimeArgs {
         path: OsPath,

vm/src/stdlib/posix.rs

@@ -901,13 +901,6 @@ pub mod module {
         nix::unistd::pipe2(oflags).map_err(|err| err.into_pyexception(vm))
     }
 
-    #[pyfunction]
-    fn system(command: PyStrRef, vm: &VirtualMachine) -> PyResult<i32> {
-        let cstr = command.to_cstring(vm)?;
-        let x = unsafe { libc::system(cstr.as_ptr()) };
-        Ok(x)
-    }
-
     fn _chmod(
         path: OsPath,
         dir_fd: DirFd<0>,