Since #5877, the checked-in nlohmann_json.natvis only covers namespaces
with up to two ABI tags. The generator gets options to produce a file
for other configurations:
- --abi-tags TAGS adds the namespaces of one configuration (repeatable)
- --all generates every combination of ABI tags
- --list-tags prints the tags with the macros that enable them
- --output FILE writes somewhere else than the repository root
`make natvis NATVIS_ARGS="..."` passes the options through. The default
output is unchanged. The options are documented in the generator's
README, the debugging page, and FILES.md, and checked in CI.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>