Fix sigaction.sa_flags type: c_int -> c_ulong

nix 0.30.1 expects SaFlags_t = c_ulong for target_os = "redox"
(see nix-0.30.1/src/sys/signal.rs:430). Our relibc had c_int,
causing type mismatch errors in uutils and any nix-dependent crate.
Align with nix's expectation.

src/platform/redox/signal.rs

@@ -127,7 +127,7 @@ impl PalSignal for Sys {
                 SigactionKind::Ignore
             } else {
                 SigactionKind::Handled {
-                    handler: if c_act.sa_flags & crate::header::signal::SA_SIGINFO as c_int != 0 {
+                    handler: if c_act.sa_flags & crate::header::signal::SA_SIGINFO as c_ulong != 0 {
                         SignalHandler {
                             sigaction: unsafe { core::mem::transmute(c_act.sa_handler) },
                         }
@@ -170,7 +170,7 @@ impl PalSignal for Sys {
                         unsafe { handler.handler }
                     },
                     sa_restorer: None,
-                    sa_flags: old_action.flags.bits() as c_int,
+                    sa_flags: old_action.flags.bits() as c_ulong,
                     sa_mask: old_action.mask,
                 },
             };