mke2fs: the -d option can now handle tarball input

mke2fs: the -d option can now handle tarball input

If archive.h is available during compilation, enable mke2fs to read a
tarball as input. Since libarchive.so.13 is opened with dlopen,
libarchive is not a hard library dependency of the resulting binary.

In comparison with feeding a directory tree to mke2fs via -d this has
the following advantages:

 - no superuser privileges, nor fakeroot, nor unshared user namespaces
   are needed to create filesystems with arbitrary ownership information
   and special files like device nodes which otherwise require being root

 - by reading a tarball from standard input, no temporary files need to
   be written out first as mke2fs can be used as part of a shell pipeline
   which reduces disk usage and makes the conversion independent of the
   underlying file system

A round-trip from tarball to ext4 to tarball yields bit-by-bit identical
results

Signed-off-by: Johannes Schauer Marin Rodrigues <josch@mister-muffin.de>