`or` alterative operator breaking windows build

Commit b44171428ab2ea25db82f7cd27349e67812e4921 introduced the `or` operator in sql/item_subselect.cc:126 . This has caused us some problems with building on windows with vs2015. I searched the code base and could not find another use of `or` as the alternative operator.

I propose removing the user of `or` and using the traditional `||`. I'll push a PR against 10.4 shortly to address this.