multilib_global: Handle PREFERRED_RPROVIDER

multilib_global: Handle PREFERRED_RPROVIDER

Running:

$ oe-selftest -r sstatetests.SStateTests.test_sstate_sametune_samesigs

after commit cdcebd81c872cb7386c658998e27cf24e1d0447c results in:

NOTE: Resolving any missing task queue dependencies
NOTE: Multiple providers are available for runtime lib32-initd-functions (lib32-initscripts, lib32-lsbinitscripts)
Consider defining a PREFERRED_RPROVIDER entry to match lib32-initd-functions

and will occasionally pick a different value on the second stamps run
causing a test failure. Update the multilib code to handle
PREFERRED_RPROVIDER too.

There is a bigger worry here which is why the builds aren't deterministic. This is
caused by a bug in bitbake's providers.py and a separate fix will be sent for that
which would cause this test to always pass or always fail.

(From OE-Core rev: ced4ac760926ce43a937dad2be3b873b1beec6aa)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>