toolchain-external: fix installation for CodeSourcery AArch64 toolchain
The extracted toolchain sources contains a single symlink in the
aarch64-linux-gnu/libc/lib directory wich is lost during Buildroot's
staging install.
aarch64-linux-gnu/libc/lib/ld-linux-aarch64.so.1 -> ../lib64/ld-2.18.so
Add a custom post install staging and target hooks to create it
manually.
Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: also make the same tweak in the target.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>