tools/coreutils: bootstrap to local gnulib source

tools/coreutils: bootstrap to local gnulib source

Using the local gnulib source during bootstrap
allows for fine-grained control over the macros
and source files for use with coreutils
but part of gnulib instead of coreutils,
without having to wait for a release
or deal with gnulib as a git submodule.

In this case, the execution of autotools
must be skipped by force.
Autoconf and Automake during bootstrap on coreutils
only works right when using directly checked-out source.

There is a symbol in gnulib, @GNULIB_TIME@
that is not yet defined in coreutils source,
so we use the backup of lib/time.in.h instead
of the one provided by gnulib source.

Signed-off-by: Michael Pratt <mcpratt@pm.me>