fix: __sigval_t causes compile error.

[Super-long]

Signed-off-by: Super-long [email protected]

I encountered the following problem when compiling：

__sigval_t has limitations, to take two different examples：
Linux VM-9-54-centos 5.4.119-1-tlinux4-0008 #1 SMP Fri Nov 26 11:17:45 CST 2021 x86_64 x86_64 x86_64 GNU/Linux

Linux VM-16-16-ubuntu 5.4.0-126-generic #142-Ubuntu SMP Fri Aug 26 12:12:57 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

This change was made for better compatibility.

[romange]

Looks good, can you please add a comment saying that __sigval_t is not compatible with some linux distributions? Otherwise I will break it again at some point. @Super-long

[Super-long]

@romange Of course, this may take a bit of time, but I will add this information soon.

[Super-long]

This continues to look like a Glibc version issue, mentioned in this document: sigval_t, although not a standard name, seems to be widely used outside of glibc.
https://patchwork.ozlabs.org/project/glibc/patch/[email protected]/

There is reason to believe that the new Glibc version will be compatible with this, and I also found the following code in glibc2.31:

So we should change __sigval_t to sigval_t.

[romange]

I agree. Can you just add a comment before DnsResolveNotify definition that says we must use sigval_t in order to support differrent glibc distributions besides ubuntu.

[Super-long]

Of course, I added some comments to explain this change.