Stripping the first char of a path to make it relative only works with
UNIX paths like '/prefix' but not with Windows paths like 'c:\prefix'.
This copies the code Meson uses.
sysconfdir defaults to /etc when the prefix is set to /usr. But joining
MESON_INSTALL_DESTDIR_PREFIX and sysconfdir when the latter is an
absoulte path, results in sysconfdir only. Which might lead to an error
during install because /etc/fonts/conf.d/ might already exist from an
pre-existing fontconfig installation.
In Makefile, we are trying to remove old symlinks first and then create a symlink.
do the same thing in meson too.
Also, the line of the exception handling for FileExistsError is meaningless
as the above line is taking care of it instead and we shouldn't ignore it if
os.remove and os.symlink doesn't work somehow.
Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/-/issues/275