LAKITU: dev-lang/python: fix sysroot incl/lib dirs

The ChromeOS cross-compile fix to setup.py doesn't implement the correct
interface in the sysroot_paths() function. It currently only returns one
path - /build/lakitu - when it should join /build/lakitu with all
provided subdirs (e.g. return [/build/lakitu/usr/include, ...]). This
change updates sysroot_paths() to do the right thing.

I'm in the process of upstreaming this change, but testing in the CrOS
environment is taking some time.

BUG=b/260587267
TEST=presubmit; `emerge-lakitu =dev-lang/python-3.8.13` and verify that
the zlib module was installed
RELEASE_NOTE=None

Change-Id: I8bdacfbe4a34506c1a4bb3e8280cac753ba8af1d
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/41461
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
3 files changed