ANDROID: kheader: kheaders: Follow symlinks to source files

When the kernel is built inside a sandbox container, a forest of
symlinks to the source files may be created in the container. In this
case, the generated kheaders.tar.xz should follow these symlinks to
access the source files, instead of packing the symlinks themselves.

Bug: 276339429
Fixes: 0b415945 ("FROMGIT: kheaders: use 'tar' instead of 'cpio' for copying files")
Link: https://lore.kernel.org/lkml/20230420010029.2702543-1-elsk@google.com/


Change-Id: Id8f3c958b0852a056f189a4e91acdded6e351606
Signed-off-by: Yifan Hong <elsk@google.com>
[cmllamas: split out flag addition into a separate commit]
Signed-off-by: Carlos Llamas <cmllamas@google.com>