Revert "Revert "FROMLIST: kheaders: Follow symlinks to source files.""

This reverts commit 3ee567fc.

Reason for revert: relanding change

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.

After this change, kheaders_data.tar.xz increases from
132K to 6.7M for Bazel builds on android-mainline.

Bug: 283225390
Bug: 276339429
Link: https://lore.kernel.org/lkml/20230420010029.2702543-1-elsk@google.com/


Signed-off-by: Yifan Hong <elsk@google.com>
Change-Id: I8fe7c02ce9a7dd355cc96df53be23dcb870e3c57