simplifying the gcc configure script to allow building of compilers that supports offloading to multiple accelerator in one go

[Mark Farnell <mark dot farnell at gmail dot com>]

As in the offloading documentation at gcc.gnu.org, currently one must
run ./configure and make for each accelerator and the host itself.
This is very inconvenient and prone to error.

Would it be possible to change the configure script so that all the
user needs to do is to:
* specify the target host architecture (if different from the build
machine architecture)
* list all accelerator architectures (such as KNL and PTX)
* specify the prefix

Then the compiler should build for the host, and all accelerator
architectures, and install binaries for both host and offload supoorts
into the prefix, taking care of relative positions between the host
and accelerator binaries.

Would this be feasible?