Add cygwin support

Author: Berrysoft

Cargo.toml

@@ -47,7 +47,7 @@ r-efi = { version = "5.1", default-features = false }
 libc = { version = "0.2.154", default-features = false }
 
 # getrandom
-[target.'cfg(any(target_os = "dragonfly", target_os = "freebsd", target_os = "hurd", target_os = "illumos", all(target_os = "horizon", target_arch = "arm")))'.dependencies]
+[target.'cfg(any(target_os = "dragonfly", target_os = "freebsd", target_os = "hurd", target_os = "illumos", target_os = "cygwin", all(target_os = "horizon", target_arch = "arm")))'.dependencies]
 libc = { version = "0.2.154", default-features = false }
 
 # netbsd
@@ -91,6 +91,7 @@ check-cfg = [
   'cfg(getrandom_test_linux_fallback)',
   'cfg(getrandom_test_linux_without_fallback)',
   'cfg(getrandom_test_netbsd_fallback)',
+  'cfg(target_os, values("cygwin"))'
 ]
 
 [package.metadata.docs.rs]

src/backends.rs

@@ -104,6 +104,7 @@ cfg_if! {
         target_os = "freebsd",
         target_os = "hurd",
         target_os = "illumos",
+        target_os = "cygwin",
         // Check for target_arch = "arm" to only include the 3DS. Does not
         // include the Nintendo Switch (which is target_arch = "aarch64").
         all(target_os = "horizon", target_arch = "arm"),

src/util_libc.rs

@@ -2,7 +2,7 @@ use crate::Error;
 use core::mem::MaybeUninit;
 
 cfg_if! {
-    if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android"))] {
+    if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android", target_os = "cygwin"))] {
         use libc::__errno as errno_location;
     } else if #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "hurd", target_os = "redox", target_os = "dragonfly"))] {
         use libc::__errno_location as errno_location;