Fix linking of generated files in cmake

If generation of files is turned off, and a file is missing, when
building in tree with cmake, you can end up with the generated file
being turned into a symlink to itself. This will also break any future
attempt at building with make. Fix this by testing if the file exists
prior to attempting to link it.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

CMakeLists.txt

@@ -131,7 +131,10 @@ function(link_to_source base_name)
         set(target "${CMAKE_CURRENT_SOURCE_DIR}/${base_name}")
     endif()
 
-    if (NOT EXISTS ${link})
+    # Linking to non-existant file is not desirable. At best you will have a
+    # dangling link, but when building in tree, this can create a symbolic link
+    # to itself.
+    if (EXISTS ${target} AND NOT EXISTS ${link})
         if (CMAKE_HOST_UNIX)
             set(command ln -s ${target} ${link})
         else()

ChangeLog.d/fix_cmake_gen_files

@@ -0,0 +1,3 @@
+Bugfix
+   * Fix an issue in releases with GEN_FILES turned off whereby missing
+     generated files could be turned into symlinks to themselves.