Auto merge of #72160 - slo1:libstd-setgroups, r=KodrAus

Add setgroups to std::os::unix::process::CommandExt

Should fix #38527. I'm not sure groups is the greatest name though.

src/test/ui/command/command-setgroups.rs

@@ -0,0 +1,26 @@
+// run-pass
+// ignore-windows - this is a unix-specific test
+// ignore-cloudabi
+// ignore-emscripten
+// ignore-sgx
+
+#![feature(rustc_private)]
+#![feature(setgroups)]
+
+extern crate libc;
+use std::process::Command;
+use std::os::unix::process::CommandExt;
+
+fn main() {
+    #[cfg(unix)]
+    run()
+}
+
+#[cfg(unix)]
+fn run() {
+    let max_ngroups = unsafe { libc::sysconf(libc::_SC_NGROUPS_MAX) };
+    let max_ngroups = max_ngroups as u32 + 1;
+    let vec: Vec<u32> = (0..max_ngroups).collect();
+    let p = Command::new("/bin/id").groups(&vec[..]).spawn();
+    assert!(p.is_err());
+}