kbuild: give up untracked files for source package builds

When the source tree is dirty and contains untracked files, package
builds may fail, for example, when a broken symlink exists, a file
path contains whitespaces, etc.

Since commit 05e96e96a315 ("kbuild: use git-archive for source package
creation"), the source tarball only contains committed files because
it is created by 'git archive'. scripts/package/gen-diff-patch tries
to address the diff from HEAD, but including untracked files by the
hand-crafted script introduces more complexity. I wrote a patch [1] to
make it work in most cases, but still wonder if this is what we should
aim for.

To simplify the code, this patch just gives up untracked files. Going
forward, it is your responsibility to do 'git add' for what you want in
the source package. The script shows a warning just in case you forgot
to do so. It should be checked only when building source packages.

[1]: https://lore.kernel.org/all/CAK7LNAShbZ56gSh9PrbLnBDYKnjtTkHMoCXeGrhcxMvqXGq9=g@mail.gmail.com/2-0001-kbuild-make-package-builds-more-robust.patch

Fixes: 05e96e96a315 ("kbuild: use git-archive for source package creation")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

kbuild: use git-archive for source package creation

Commit 5c3d1d0abb12 ("kbuild: add a tool to list files ignored by git")
added a new tool, scripts/list-gitignored. My intention was to create
source packages without cleaning the source tree, without relying on git.

Linus strongly objected to it, and suggested using 'git archive' instead.
[1] [2] [3]

This commit goes in that direction - Remove scripts/list-gitignored.c
and rewrites Makefiles and scripts to use 'git archive' for building
Debian and RPM source packages. It also makes 'make perf-tar*-src-pkg'
use 'git archive' again.

Going forward, building source packages is only possible in a git-managed
tree. Building binary packages does not require git.

[1]: https://lore.kernel.org/lkml/CAHk-=wi49sMaC7vY1yMagk7eqLK=1jHeHQ=yZ_k45P=xBccnmA@mail.gmail.com/
[2]: https://lore.kernel.org/lkml/CAHk-=wh5AixGsLeT0qH2oZHKq0FLUTbyTw4qY921L=PwYgoGVw@mail.gmail.com/
[3]: https://lore.kernel.org/lkml/CAHk-=wgM-W6Fu==EoAVCabxyX8eYBz9kNC88-tm9ExRQwA79UQ@mail.gmail.com/

Fixes: 5c3d1d0abb12 ("kbuild: add a tool to list files ignored by git")
Fixes: e0ca16749ac3 ("kbuild: make perf-tar*-src-pkg work without relying on git")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>