[bug-gnulib] canonicalize.c and realpath

[Eric Blake]

Currently, lib/canonicalize.c performs a configure check to see if 
resolvepath(2) is exported, to speed up canonicalize_file_name.  This is not a 
POSIX function, and meanwhile POSIX XSI requires realpath(2) to exist 
(basically, resolvepath without the length argument).  Some systems, like 
cygwin, have realpath but not resolvepath, but gnulib is not even checking for 
realpath.  Also, some implementations of realpath malloc memory if the 
destination is NULL, similar to getcwd.  I don't have copyright assignment yet, 
or I would propose a patch to canonicalize to support realpath.  Should we also 
add a realpath module to provide realpath on systems that don't have it?

--
Eric Blake