[Bug libstdc++/91486] future::wait_for and shared_timed_mutex::wait_for do not work properly with float duration

[mac at mcrowe dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91486

--- Comment #11 from Mike Crowe <mac at mcrowe dot com> ---
Created attachment 49305
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49305&action=edit
Small fix to f9ddb696a289cc48d24d3d23c0b324cb88de9573