https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90299
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I changed absolute("", ec) to return an error intentionally, and I think
absolute("") should also return an error.
The effects of the function are to "compose an absolute path referencing the
same file system location as p". When p is the empty path it does not reference
any file system location, and so the function cannot meet its postcondition,
and must report an error.
The bug is that r260441 only fixed the overload taking an error_code&
parameter.
