timeout: disable pre-existing SIGCHLD handlers

Needed to make a GNU test pass

Cargo.lock

@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "Inflector"
 version = "0.11.4"
@@ -2606,6 +2608,7 @@ version = "0.0.6"
 dependencies = [
  "clap",
  "libc",
+ "nix 0.20.0",
  "uucore",
  "uucore_procs",
 ]

src/uu/timeout/Cargo.toml

@@ -17,6 +17,7 @@ path = "src/timeout.rs"
 [dependencies]
 clap = "2.33"
 libc = "0.2.42"
+nix = "0.20.0"
 uucore = { version=">=0.0.8", package="uucore", path="../../uucore", features=["parse_time", "process", "signals"] }
 uucore_procs = { version=">=0.0.5", package="uucore_procs", path="../../uucore_procs" }
 

src/uu/timeout/src/timeout.rs

@@ -5,7 +5,7 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) tstr sigstr cmdname setpgid
+// spell-checker:ignore (ToDO) tstr sigstr cmdname setpgid sigchld
 
 #[macro_use]
 extern crate uucore;
@@ -161,6 +161,17 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     )
 }
 
+/// Remove pre-existing SIGCHLD handlers that would make waiting for the child's exit code fail.
+fn unblock_sigchld() {
+    unsafe {
+        nix::sys::signal::signal(
+            nix::sys::signal::Signal::SIGCHLD,
+            nix::sys::signal::SigHandler::SigDfl,
+        )
+        .unwrap();
+    }
+}
+
 /// TODO: Improve exit codes, and make them consistent with the GNU Coreutils exit codes.
 
 fn timeout(
@@ -194,6 +205,7 @@ fn timeout(
             }
         }
     };
+    unblock_sigchld();
     match process.wait_or_timeout(duration) {
         Ok(Some(status)) => status.code().unwrap_or_else(|| status.signal().unwrap()),
         Ok(None) => {