Add sigqueue

Author: yshui

libc-test/semver/unix.txt

@@ -795,6 +795,7 @@ sigismember
 signal
 sigpending
 sigprocmask
+sigqueue
 sigset_t
 sigval
 size_t

src/unix/mod.rs

@@ -1674,6 +1674,17 @@ cfg_if! {
     }
 }
 
+cfg_if! {
+    if #[cfg(not(any(
+        target_os = "emscripten",
+        target_os = "macos",
+    )))] {
+        extern "C" {
+            pub fn sigqueue(pid: pid_t, sig: c_int, value: crate::sigval) -> c_int;
+        }
+    }
+}
+
 cfg_if! {
     if #[cfg(not(target_os = "android"))] {
         extern "C" {