mandb warnings with some operators

[cschreib]

When installing, and running sudo mandb, I get:

mandb: warning: failed to store entry for std::filesystem::directory_entry::operator==,!=,,>=,(3)
mandb: warning: failed to store entry for std::type_index::operator==,!=,,>=,(3)
mandb: warning: failed to store entry for std::chrono::operator==,,>=,(std::chrono::leap_second)(3)
mandb: warning: failed to store entry for std::experimental::filesystem::directory_entry::operator==,!=,,>=(3)

The corresponding documentation is for, e.g.:

It seems that operators < and > are somehow missing in the warning text ==,!=,,>=,, which perhaps explains the problem.