[Bug c++/81513] __has_cpp_attribute returns non-zero in C++03 mode, but attributes don't work

[proski at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81513

--- Comment #2 from Pavel Roskin <proski at gnu dot org> ---
__has_cpp_attribute is not supposed to check if the functionality is available
somehow using some other approaches and keywords. It is supposed to check if
the functionality is available as an attribute.

Even is there is some alternative notation for C++03, I expect the attribute
name to be the same. If __has_cpp_attribute(maybe_unused) is set to a non-zero
value, I expect to use "maybe_unused", not "unused".