[OE-core] [PATCH v4 2/4] cmake.bbclass: search both sysroot-native and host for native packages

[Burton, Ross]

I think I figured out why we're seeing odd failures on the
autobuilder, such as
https://autobuilder.yoctoproject.org/typhoon/#/builders/15/builds/125.

The important bit of the log is:

File "/home/pokybuild/yocto-worker/poky-tiny/build/build/tmp/work/qemux86-poky-linux-musl/core-image-minimal/1.0-r0/recipe-sysroot-native/usr/lib/python3.5/site-packages/libcomps/__init__.py",
line 1, in <module>
from ._libpycomps import *
ImportError: libpython3.6m.so.1.0: cannot open shared object file: No
such file or directory

The smoking gun is that oe-core doesn't have Python 3.6, but 3.5.

My suspicion is that for systems where the host has python3-devel
installed, libcomp-native's cmake is using the host python instead of
the native python in the sysroot.  I'm not sure yet if BOTH means it
searches the host before the sysroots, or if it is finding the python
binary in HOSTTOOLS and then asking that what the paths are.  Either
way, it ends up linking to the host libpython3.5.so and going into
sstate.  Another machine in the pool reuses this sstate but it doesn't
have Python 3.6 installed, so the library link is broken.

Ross