CI: mask poky's llvm if we're using clang

meta-clang's clang recipe has an irritating interaction with oe-core's
llvm recipe which can result in build warnings, which cause builds to
fail in our pedantic CI.

The current best known workaround is to simply mask out the llvm recipes
if clang is being used.

For more details, see https://github.com/kraj/meta-clang/pull/766.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/clang.yml

@@ -8,3 +8,6 @@ repos:
 local_conf_header:
   toolchain: |
     TOOLCHAIN = "clang"
+    # This is needed to stop bitbake getting confused about what clang/llvm is
+    # being used, see https://github.com/kraj/meta-clang/pull/766
+    BBMASK += "/meta/recipes-devtools/llvm/llvm.*\.bb"