cooker: only append files once

A list can contain the same value twice, therefore only append to the
appendlist for a recipe if the append file is not already in the list.

(Bitbake rev: d11f9dd33cdcc97a4a937e8bf7e97558d813cadd)

Signed-off-by: Joshua Lock <josh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -1212,7 +1212,8 @@ class BBCooker:
             base = os.path.basename(f).replace('.bbappend', '.bb')
             if not base in self.appendlist:
                self.appendlist[base] = []
-            self.appendlist[base].append(f)
+            if f not in self.appendlist[base]:
+                self.appendlist[base].append(f)
 
         # Find overlayed recipes
         # bbfiles will be in priority order which makes this easy