Rollup merge of #145673 - Berrysoft:cygwin-fix-flock, r=joshtriplett

Add flock support for cygwin

See discussion: #145534 (comment)

cc: ``@jeremyd2019``

Author: jhpratt

library/std/src/sys/fs/unix.rs

@@ -1265,6 +1265,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     ))]
     pub fn lock(&self) -> io::Result<()> {
@@ -1278,6 +1279,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     )))]
     pub fn lock(&self) -> io::Result<()> {
@@ -1290,6 +1292,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     ))]
     pub fn lock_shared(&self) -> io::Result<()> {
@@ -1303,6 +1306,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     )))]
     pub fn lock_shared(&self) -> io::Result<()> {
@@ -1315,6 +1319,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     ))]
     pub fn try_lock(&self) -> Result<(), TryLockError> {
@@ -1336,6 +1341,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     )))]
     pub fn try_lock(&self) -> Result<(), TryLockError> {
@@ -1351,6 +1357,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     ))]
     pub fn try_lock_shared(&self) -> Result<(), TryLockError> {
@@ -1372,6 +1379,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     )))]
     pub fn try_lock_shared(&self) -> Result<(), TryLockError> {
@@ -1387,6 +1395,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     ))]
     pub fn unlock(&self) -> io::Result<()> {
@@ -1400,6 +1409,7 @@ impl File {
         target_os = "linux",
         target_os = "netbsd",
         target_os = "openbsd",
+        target_os = "cygwin",
         target_vendor = "apple",
     )))]
     pub fn unlock(&self) -> io::Result<()> {