std: add seteuid/setegid to std.os

Currently these are only implemented for linux.

lib/std/os.zig

@@ -2512,11 +2512,12 @@ pub fn readlinkatZ(dirfd: fd_t, file_path: [*:0]const u8, out_buffer: []u8) Read
     }
 }
 
-pub const SetIdError = error{
+pub const SetEidError = error{
-    ResourceLimitReached,
     InvalidUserId,
     PermissionDenied,
-} || UnexpectedError;
+};
+
+pub const SetIdError = error{ResourceLimitReached} || SetEidError || UnexpectedError;
 
 pub fn setuid(uid: uid_t) SetIdError!void {
     switch (errno(system.setuid(uid))) {
@@ -2528,6 +2529,15 @@ pub fn setuid(uid: uid_t) SetIdError!void {
     }
 }
 
+pub fn seteuid(uid: uid_t) SetEidError!void {
+    switch (errno(system.seteuid(uid))) {
+        0 => return,
+        EINVAL => return error.InvalidUserId,
+        EPERM => return error.PermissionDenied,
+        else => |err| return unexpectedErrno(err),
+    }
+}
+
 pub fn setreuid(ruid: uid_t, euid: uid_t) SetIdError!void {
     switch (errno(system.setreuid(ruid, euid))) {
         0 => return,
@@ -2548,6 +2558,15 @@ pub fn setgid(gid: gid_t) SetIdError!void {
     }
 }
 
+pub fn setegid(uid: uid_t) SetEidError!void {
+    switch (errno(system.setegid(uid))) {
+        0 => return,
+        EINVAL => return error.InvalidUserId,
+        EPERM => return error.PermissionDenied,
+        else => |err| return unexpectedErrno(err),
+    }
+}
+
 pub fn setregid(rgid: gid_t, egid: gid_t) SetIdError!void {
     switch (errno(system.setregid(rgid, egid))) {
         0 => return,