[OE-core] meta-toolchain / /bin/sh requirement / ldconfig backfill

[Mark Hatle]

I tried to build the meta-toolchain, toolchain SDK today and received an error.
My system is configured to use package_rpm by default...

The error I got was:

Error:
 Problem: package
          packagegroup-core-standalone-sdk-target-1.0-r8.noarch requires
          libstdc++6, but none of the providers can be installed
  - conflicting requests
  - nothing provides /bin/sh needed by libstdc++6-7.2.0-r0.i586


The /bin/sh dependency seems kind of odd at first, but after a little research
it turns out that by default 'ldconfig' support is now enabled.  This
automatically adds a post-install script to any package with a library in it:

#!/bin/sh
if [ x"$D" = "x" ]; then
        if [ -x /sbin/ldconfig ]; then /sbin/ldconfig ; fi
fi


That in-turn causes the dependency of /bin/sh to occur.

Because of this, there is no way (with a default configuration) to build
meta-toolchain....

Investigating further, ldconfig support moved from "USE_LDCONFIG" to a
distribution configuration.  It does this via the "DISTRO_FEATURES_BACKFILL"
(introduced in commit: a905df2dd8f43a2febffa64a39b6e508510326a0)


If I add to my configuration:

 DISTRO_FEATURES_BACKFILL_CONSIDERED_append = " ldconfig"

This works around the issue...  but doesn't resolve the default issue....

So my question is, is this behavior (the failure case) really acceptable without
telling the user what is happening?  Or do we need to add something to the
system that says meta-toolchain can't be used with this DISTRO_FEATURE?  or...

--Mark