Check how to make a copy by creating a symbolic link to the original -
it defines the variable CP_S for further use, which you should in fact
treat like it used to be with be LN_S. The actual value is assured to be
either LN_S (if the filesystem supports symbolic links) or CP (if the
filesystem does not know about symbolic links and you need a copy of
original file to have the same text in both places).
In a gnu environment it will simply set CP_S="cp -s" since the gnu
"cp"-command has the "-s" flag. You shall not try to use this
command on directories since it would require a "-r" in the case of
a copy that is not supported explicitly here. (I'm not sure if some
"cp"-commands out there would barf at usage of "-r" on a normal file).
Use CP_S to create a copy of read-only data - if your filesystem
supports it then a symbolic link is created - a process that is
quicker and space-saving. However, if the target fs does not
support symbolic links, just copy the data. Unlike ac_prog_ln_s
this macro will never fail to set the CP_S ac_subst to something