unicode: fix .gitignore for generated utfdata file

Commit 2b3d04787012 ("unicode: Add utf8-data module") changed the
generated utf8data file from 'utf8data.h' to 'utf8data.c', but didn't
change the comments or the .gitignore to match.

The comments should be updated too, but at least they don't cause any
visible breakage. But the gitignore file needs changing to avoid git
complaining about untracked files.

Fixes: 2b3d04787012 ("unicode: Add utf8-data module")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

.gitignore: prefix local generated files with a slash

The pattern prefixed with '/' matches files in the same directory,
but not ones in sub-directories.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Andra Paraschiv <andraprs@amazon.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Gabriel Krisman Bertazi <krisman@collabora.com>

.gitignore: add SPDX License Identifier

Add SPDX License Identifier to all .gitignore files.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

unicode: refactor the rule for regenerating utf8data.h

scripts/mkutf8data is used only when regenerating utf8data.h,
which never happens in the normal kernel build. However, it is
irrespectively built if CONFIG_UNICODE is enabled.

Moreover, there is no good reason for it to reside in the scripts/
directory since it is only used in fs/unicode/.

Hence, move it from scripts/ to fs/unicode/.

In some cases, we bypass build artifacts in the normal build. The
conventional way to do so is to surround the code with ifdef REGENERATE_*.

For example,

- 7373f4f83c71 ("kbuild: add implicit rules for parser generation")
- 6aaf49b495b4 ("crypto: arm,arm64 - Fix random regeneration of S_shipped")

I rewrote the rule in a more kbuild'ish style.

In the normal build, utf8data.h is just shipped from the check-in file.

$ make
[ snip ]
SHIPPED fs/unicode/utf8data.h
CC fs/unicode/utf8-norm.o
CC fs/unicode/utf8-core.o
CC fs/unicode/utf8-selftest.o
AR fs/unicode/built-in.a

If you want to generate utf8data.h based on UCD, put *.txt files into
fs/unicode/, then pass REGENERATE_UTF8DATA=1 from the command line.
The mkutf8data tool will be automatically compiled to generate the
utf8data.h from the *.txt files.

$ make REGENERATE_UTF8DATA=1
[ snip ]
HOSTCC fs/unicode/mkutf8data
GEN fs/unicode/utf8data.h
CC fs/unicode/utf8-norm.o
CC fs/unicode/utf8-core.o
CC fs/unicode/utf8-selftest.o
AR fs/unicode/built-in.a

I renamed the check-in utf8data.h to utf8data.h_shipped so that this
will work for the out-of-tree build.

You can update it based on the latest UCD like this:

$ make REGENERATE_UTF8DATA=1 fs/unicode/
$ cp fs/unicode/utf8data.h fs/unicode/utf8data.h_shipped

Also, I added entries to .gitignore and dontdiff.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>