[0/8] AIX cross toolchains

[Richard Sandiford <richards at transitive dot com>]

This series of patches adds support for AIX-targetted cross toolchains.
As with other cross toolchains for "hosted" systems, the assumption is
that you have an AIX sysroot available and are using --with-sysroot to
point to it.  (This assumption also implicitly requires GNU ld, with its
support for --sysroot.)

Until recently, binutils could not build working AIX shared libraries,
so the patches only work with a CVS copy of binutils.  And because of
the binutils problems, current libtool doesn't let you try to use
binutils to build AIX shared libraries; it will always switch to
static libraries instead.  The following patches remove this
restriction:

    http://lists.gnu.org/archive/html/libtool-patches/2009-03/msg00007.html
    http://lists.gnu.org/archive/html/libtool-patches/2009-04/msg00013.html

The patches haven't been accepted, so you'll need to apply them locally
and then regenerate each configure script.

All patches were tested by:

  - A native bootstrap on powerpc-ibm-aix6.1 using binutils, with a hack
    to disable the stuff in config/mh-ppc-aix.  Test flags: {,-pthread}.
    (I couldn't test for -maix64 for reasons explained in patch 8.)

  - A native boostrap on x86_64-linux-gnu.  Test flags: {,-m32}.

  - A cross build and cross test from x86_64-linux-gnu to
    powerpc-ibm-aix6.1.  Test flags: {,-pthread}{,-maix64}.

The patches are covered by the IBM copyright assignment.

Richard