e2fsprogs: break out libcomerr/libss, FS#1310

libext2fs breaks krb5 by always installing its own copies of libcom_err.so
and libss.so.

Move the libraries into separate libcomerr and libss packages respectively
and add a host build recipe to stage the required compile_et and mk_cmds
utilities for use by other packages.

This allows the krb5 package to be fixed to use the system wide libcomerr
and libss libraries.

Signed-off-by: Andy Walsh <andy.walsh44+github@gmail.com>
[rename libcom_err to libcomerr, make compile_et and mk_cmds relocatable,
 cleanup makefile, add dependency on host build, reword commit message]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>