Fix Issue 8663 - AliasThis is not used in comparison

[RazvanN7]

The function compare_overload searches for opCmp or opEquals and if it finds a user defined one it picks, however, for classes it always finds the one defined in object.d and it does not check the alias this.

[dlang-bot]

Thanks for your pull request and interest in making D better, @RazvanN7! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the annotated coverage diff directly on GitHub with CodeCov's browser extension
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	8663	normal	AliasThis is not used in comparison

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#8976"

[thewilsonator]

Please rewrite this as

const bool cond /* better name needed*/ = lastf && m.lastf == lastf || !s_r && m.last <= MATCH.nomatch;
auto opfunc = cond ? s : s_r;
uint errors = global.startGagging();
result = build_overload(e.loc, sc, e.e1, e.e2, m.lastf ? m.lastf : opfunc);
if (global.endGagging(errors))
{
     result = checkAliasThisForLhs(ad1, sc, e);
     if (result)
           return result;
     result = checkAliasThisForRhs(ad2, sc, e);
     if (result)
          return result;
}
result = build_overload(e.loc, sc, e.e1, e.e2, m.lastf ? m.lastf : opfunc);
if (!cond)
switch(e.op)
{
     ...
}

[WalterBright]

This is another manifestation of https://issues.dlang.org/show_bug.cgi?id=5380

I'm not sure we should be fixing this.