sanity.conf: Bump bitbake requirement to 2.15.0

This brings in the features we need to toolchain selection.

(From OE-Core rev: 78c1061dc3916677bd9c2825820a1bab7e75f28a)

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

meta/conf/sanity.conf

@@ -3,7 +3,7 @@
 # See sanity.bbclass
 #
 # Expert users can confirm their sanity with "touch conf/sanity.conf"
-BB_MIN_VERSION = "2.12.0"
+BB_MIN_VERSION = "2.15.0"
 
 SANITY_ABIFILE = "${TMPDIR}/abi_version"