archiver: fix gcc-source handling

archiver: fix gcc-source handling

The source archiver was not handling the gcc-source target correctly, since it uses the
work-shared directory, we don't want to unpack and patch it twice, just as the comments
say, but the code was not there to check for the gcc-source target.

[YOCTO #10265]

Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>