Remove AA comparison from std.xml

The compiler has historically been doing a cast(void *) for AA compares,
which doesn't make much sense. Make it explicit to preserve existing
behaviour, until this module is replaced.
Merge pull request #1599 from donc/aa10381xml

Remove AA comparison from std.xml
Fix FunctionAttribute DDoc
Merge pull request #1600 from monarchdodra/FunctionAttributeDDoc

Fix FunctionAttribute DDoc