\w, $PWD and pwd builtin return "//" instead of '/'

[mike b]

Upon changing directory, with "//" passed as an argument, the trailing '/'
is still displayed when cwd is looked up by Bash:

bash-5.0# cd //
bash-5.0# pwd
//
bash-5.0# echo $PWD
//
bash-5.0# PS1=${PS1/\$/\w\\$}
bash-5.0//# # \w -> "//"
bash-5.0//# /bin/pwd  # <- coreutils implementation
/
bash-5.0//#

This seems to happen only when number of '/' char == 2, anything > 2 is
properly displayed as single '/' char.

Same is observed in 4.4.12.