IVGCVSW-1921: move common Acl code to a separate folder

Change-Id: I400be8e7c0cc5a31eb9d2a7396da145d50d51b6e
diff --git a/src/backends/backends.cmake b/src/backends/backends.cmake
index 462365c..6f76106 100644
--- a/src/backends/backends.cmake
+++ b/src/backends/backends.cmake
@@ -7,9 +7,11 @@
 list(APPEND armnnLibraries armnnBackendsCommon)
 
 # single place to use wildcards, so we can include
-# yet unknown backend modules
+# yet unknown backend modules and corresponding common libraries
+FILE(GLOB commonIncludes ${PROJECT_SOURCE_DIR}/src/backends/*/common.cmake)
 FILE(GLOB backendIncludes ${PROJECT_SOURCE_DIR}/src/backends/*/backend.cmake)
 
-foreach(backendInclude ${backendIncludes})
+# prefer to include common code first so backends can depend on them
+foreach(backendInclude ${commonIncludes} ${backendIncludes})
     include(${backendInclude})
 endforeach()