[OE-core] Shared work directory proof of concept

[Richard Purdie]

One of the items on the 1.1 feature list is sharing work directories.
This is desirable for example for gcc where the same sources are
unpacked and patched for gcc-cross-initial, gcc-cross-intermediate,
gcc-cross, gcc-runtime and so on.

I've done a little experimentation with this and the code linked to
below shows its at least possible and the kind of changes we might need
to make to bitbake to support it:

http://git.yoctoproject.org/cgit.cgi/poky-contrib/commit/?h=rpurdie/gcc-sharedwork&id=4a22c2212466ef3bcb20960b1f99f8509347b24d

There are at least 4 issues I've noted in the commit which we'd need to
to look before we could start using this code, nothing impossible
though, just needs more work.

Cheers,

Richard