build: regenerate config-list.h when Documentation changes

The Meson-based build doesn't know when to rebuild config-list.h, so the header is sometimes stale. For example, an old build directory might have config-list.h from before 4173df5187 (submodule: introduce extensions.submodulePathConfig, 2026-01-12), which added submodule.<name>.gitdir to the list. Without it, t9902-completion.sh fails. Regenerating the config-list.h artifact from sources fixes the artifact and the test. Since Meson does not have (or want) builtin support for globbing like Make, teach generate-configlist.sh to also generate a list of Documentation files its output depends on, and incorporate that into the Meson build. We honor the undocumented GCC/Clang contract of outputting empty targets for all the dependencies (like they do with -MP). That is, generate lines like build/config-list.h: $SOURCE_DIR/Documentation/config.adoc $SOURCE_DIR/Documentation/config.adoc: We assume that if a user adds a new file under Documentation/config then they will also edit one of the existing files to include that new file, and that will trigger a rebuild. Also mark the generator script as a dependency. While we're at it, teach the Makefile to use the same "the script knows it's dependencies" logic. For Meson, combining the following commands helps debug dependencies: ninja -C <builddir> -t deps config-list.h ninja -C <builddir> -t browse config-list.h The former lists all the dependencies discovered from our output ".d" file (the config documentation) and the latter shows the dependency on the script itself, among other useful edges in the dependency graph. Helped-by: Patrick Steinhardt <ps@pks.im> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>