host-autoconf-archive: install to a non-standard location

The host-autoconf-archive package was added to provide the necessary
autoconf macros for the libsigrok package, and later also used for the
thrift package.

However, it installs its autoconf macro in
$(HOST_DIR)/usr/share/aclocal, which is part of the include directory
of autoconf macros used for all autoreconf invocations. Unfortunately,
using those macros for all packages is causing a number of
regressions: one on host-ola fixed in commit
884af65f, and one in snmpp. Those
packages are autoreconf'ed, but if they are autoreconf'ed with the
autoconf-archive macros installed, they no longer work.

To solve this problem, this commit implements a simple solution that
makes using host-autoconf-archive macros an opt-in mechanism. To
achieve this, the autoconf-archive package is modified to install its
macros in a special directory, and only the packages that really want
to use those macros will have to pass a -I flag pointing to this
directory in their <pkg>_AUTORECONF_OPTS variable.

Fixes:

  http://autobuild.buildroot.org/results/712/712c8083b9eeafa41b60790961028c40b28f59ad/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Romain Naour <romain.naour@openwide.fr>
Tested-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>