[version 3.4] Linker scripts do not define _end correctly

[keith-packard]

In version 3.4, The various sample linker scripts do not define _end correctly or consistently. This breaks code using this symbol, such as the common malloc implementation. This has been fixed upstream in #57727 which should be backported.

[fabiobaltieri]

Hey @keith-packard, 3.4 has been unsupported for a while, closing this down.