more test fixups, phrasing

Author: Jan Philipp Hafer

lib/std/child_process.zig

@@ -339,7 +339,7 @@ pub const ChildProcess = struct {
 
     fn waitUnwrappedPosix(self: *ChildProcess) !void {
         const res: os.posix.WaitPidResult = if (comptime builtin.target.isDarwin())
-            try os.posix_spawn.waitpid(self.pid, 0)
+            try os.posix_spawn.waitpid(self.id, 0)
         else
             os.posix.waitpid(self.id, 0);
         const status = res.status;

lib/std/fs/file.zig

@@ -409,7 +409,7 @@ pub const File = struct {
         try os.posix.fchmod(self.handle, new_mode);
     }
 
-    pub const ChownError = std.os.FChownError;
+    pub const ChownError = std.os.posix.FChownError;
 
     /// Changes the owner and group of the file.
     /// The process must have the correct privileges in order to do this

lib/std/os/posix.zig

@@ -1,6 +1,7 @@
 //! This file contains posix abstractions and wrappers around
 //! OS-specific APIs for conforming platforms, whether libc is or is not linked.
-//! APIs defined here can not have comparable semantics on Windows.
+//! Purpose is to have error handling for APIs, which can not have comparable
+//! semantics on non-posix systems like Windows.
 
 const std = @import("std");
 const builtin = @import("builtin");