configure: remove BeOS support

Likely doesn't work anymore anyway.
configure: prepare for hybrid support

The goal is to do hybrid builds in a single jam (instead of calling a
sub-jam to build parts with the secondary tool chain). This changeset
adds support to configure to prepare multiple tool chains.

configure:
* Merge option --build-cross-tools-gcc4 into --build-cross-tools. The
  option does now always require a packaging architecture parameter,
  i.e. x86_gcc2 for the legacy tool chain.
* Multiple occurrences of the --build-cross-tools and
  --cross-tools-prefix options are allowed. The first one specifies the
  primary tool chain, the subsequent ones the secondary tool chains.
* All architecture dependent jam variables are now suffixed with the
  name of the packaging architecture. The new HAIKU_PACKAGING_ARCHS
  contains the packaging architectures for the prepared tool chains. The
  first element is for the primary tool chain.
* No longer generate a separate libgccObjects file. Just put the
  respective variable into BuildConfig as well.

build_cross_tools[_gcc4]:
* Replace the <haiku output dir> parameter by a <install dir>
  parameter. This allows to create different cross-tools directories.
  They are simply suffixed by the packaging architecture.

Jamrules:
* For the moment map the variables for the primary tool chain to the
  respective suffix-less variables, so that everything still works as
  before.

The next step is to actually support the secondary tool chains in the
jam build system. This will require quite a bit more butchering, though.