unit-test: add workaround for clang-20 errors

We are seeing pervasive issues with clang-20 with boost async_wait
calls mixed with std::bind_front:

```
/usr/local/include/sdbusplus/asio/connection.hpp:411:15: error: no matching member function for call to 'async_wait'
  411 |         timer.async_wait(std::bind_front(&connection::on_timer_event, this));
```

This issue is noted upstream[1] and is currently unsolved, but we
discovered we can solve this by passing `-fno-builtin-std-forward_like`
as a clang compiler option.  Add this to the unit-test scripts when
the `CXX` is clang.

[1]: https://github.com/llvm/llvm-project/issues/101614

Tested: Ran locally against dbus-sensors and observed the compile
issues are resolved.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3e5a68320df10fd835613da452c0fcefa95e6a22
1 file changed