build: allow cros-compilation on chromeOS

- Request LIBTOOL to be used
- Set topbuildir based on a Makefile variable to call libtool
- Use /usr/local instead of /var for xfstest final location
- Move macros from aclocal.m4 to acinclude.m4, aclocal.m4 is autogenerated.
- Use autoconf variables @prefix@, @exec_prefix@.

The regular way of compiling xfstests - make - remains.
But it now runs autoreconf and libtoolize -i to produce a valid
configure.
Verified with 'make install --dry-run' that files are installed at the
same place.
Verified compiling in chromeOS chroot works as well.

[eguan: resolve merge conflicts and update .gitignore and remove
generated files by realclean]

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
7 files changed