Impl cygwin rand with getrandom

library/std/src/sys/random/cygwin.rs

@@ -0,0 +1,8 @@
+pub fn fill_bytes(mut bytes: &mut [u8]) {
+    while !bytes.is_empty() {
+        let ret =
+            unsafe { libc::getrandom(bytes.as_mut_ptr().cast(), bytes.len(), libc::GRND_NONBLOCK) };
+        assert!(ret != -1, "failed to generate random data");
+        bytes = &mut bytes[ret as usize..];
+    }
+}

library/std/src/sys/random/linux.rs

@@ -94,14 +94,7 @@ fn getrandom(
 
             let flags = if insecure {
                 if GRND_INSECURE_AVAILABLE.load(Relaxed) {
-                    #[cfg(target_os = "cygwin")]
-                    {
-                        libc::GRND_NONBLOCK
-                    }
-                    #[cfg(not(target_os = "cygwin"))]
-                    {
-                        libc::GRND_INSECURE
-                    }
+                    libc::GRND_INSECURE
                 } else {
                     libc::GRND_NONBLOCK
                 }
@@ -117,7 +110,6 @@ fn getrandom(
                     libc::EINTR => continue,
                     // `GRND_INSECURE` is not available, try
                     // `GRND_NONBLOCK`.
-                    #[cfg(not(target_os = "cygwin"))]
                     libc::EINVAL if flags == libc::GRND_INSECURE => {
                         GRND_INSECURE_AVAILABLE.store(false, Relaxed);
                         continue;

library/std/src/sys/random/mod.rs

@@ -1,11 +1,14 @@
 cfg_if::cfg_if! {
     // Tier 1
-    if #[cfg(any(target_os = "linux", target_os = "android", target_os = "cygwin"))] {
+    if #[cfg(any(target_os = "linux", target_os = "android"))] {
         mod linux;
         pub use linux::{fill_bytes, hashmap_random_keys};
     } else if #[cfg(target_os = "windows")] {
         mod windows;
         pub use windows::fill_bytes;
+    } else if #[cfg(target_os = "cygwin")] {
+        mod cygwin;
+        pub use cygwin::fill_bytes;
     } else if #[cfg(target_vendor = "apple")] {
         mod apple;
         pub use apple::fill_bytes;
@@ -88,7 +91,6 @@
     target_os = "android",
     all(target_family = "wasm", target_os = "unknown"),
     target_os = "xous",
-    target_os = "cygwin",
 )))]
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut buf = [0; 16];