Fix comments for os_* functions return value

In windows libuv does not return -errno, instead it uses negative
error codes e.g. UV_ENOENT. This commit changes the comments in os_*
functions to reflect this.

src/nvim/event/socket.c

@@ -97,7 +97,7 @@ int socket_watcher_start(SocketWatcher *watcher, int backlog, socket_cb cb)
     result = uv_listen(watcher->stream, backlog, connection_cb);
   }
 
-  assert(result <= 0);  // libuv should have returned -errno or zero.
+  assert(result <= 0);  // libuv should return negative error code or zero.
   if (result < 0) {
     if (result == -EACCES) {
       // Libuv converts ENOENT to EACCES for Windows compatibility, but if

src/nvim/event/stream.c

@@ -13,7 +13,7 @@
 
 /// Sets the stream associated with `fd` to "blocking" mode.
 ///
-/// @return `0` on success, or `-errno` on failure.
+/// @return `0` on success, or libuv error code on failure.
 int stream_set_blocking(int fd, bool blocking)
 {
   // Private loop to avoid conflict with existing watcher(s):

src/nvim/os/fs.c

@@ -185,13 +185,13 @@ static bool is_executable_in_path(const char_u *name, char_u **abspath)
 
 /// Opens or creates a file and returns a non-negative integer representing
 /// the lowest-numbered unused file descriptor, for use in subsequent system
-/// calls (read, write, lseek, fcntl, etc.). If the operation fails, `-errno`
-/// is returned, and no file is created or modified.
+/// calls (read, write, lseek, fcntl, etc.). If the operation fails, a libuv
+/// error code is returned, and no file is created or modified.
 ///
 /// @param flags Bitwise OR of flags defined in <fcntl.h>
 /// @param mode Permissions for the newly-created file (IGNORED if 'flags' is
 ///        not `O_CREAT` or `O_TMPFILE`), subject to the current umask
-/// @return file descriptor, or negative `errno` on failure
+/// @return file descriptor, or libuv error code on failure
 int os_open(const char* path, int flags, int mode)
   FUNC_ATTR_NONNULL_ALL
 {
@@ -322,7 +322,7 @@ int os_rename(const char_u *path, const char_u *new_path)
 
 /// Make a directory.
 ///
-/// @return `0` for success, -errno for failure.
+/// @return `0` for success, libuv error code for failure.
 int os_mkdir(const char *path, int32_t mode)
   FUNC_ATTR_NONNULL_ALL
 {
@@ -342,7 +342,7 @@ int os_mkdir(const char *path, int32_t mode)
 ///                          failed to create. I.e. it will contain dir or any
 ///                          of the higher level directories.
 ///
-/// @return `0` for success, -errno for failure.
+/// @return `0` for success, libuv error code for failure.
 int os_mkdir_recurse(const char *const dir, int32_t mode,
                      char **const failed_dir)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT

src/nvim/os/fs_defs.h

@@ -21,9 +21,9 @@ typedef struct {
   uv_dirent_t ent;  ///< @private The entry information.
 } Directory;
 
-/// Function to convert -errno error to char * error description
+/// Function to convert libuv error to char * error description
 ///
-/// -errno errors are returned by a number of os functions.
+/// negative libuv error codes are returned by a number of os functions.
 #define os_strerror uv_strerror
 
 #endif  // NVIM_OS_FS_DEFS_H

src/nvim/os/os_defs.h

@@ -103,9 +103,9 @@
 # include <strings.h>
 #endif
 
-/// Function to convert -errno error to char * error description
+/// Function to convert libuv error to char * error description
 ///
-/// -errno errors are returned by a number of os functions.
+/// negative libuv error codes are returned by a number of os functions.
 #define os_strerror uv_strerror
 
 #endif  // NVIM_OS_OS_DEFS_H