./configure --help should print --disable-docs instead of --enable-docs

[dilyanpalauzov]

With rust 1.82 ./configure --help prints:

        --enable-docs                  build standard library documentation 

This suggests, that by default the standard library documentation is not built, but with this option it can be turned on. If the --help output was

        --disable-docs                  do not build standard library documentation 

this would have suggested, that by default the documentation is built. Cf. https://ab.bapha.be/posts/help-output/)

config.example.toml contains

# Whether to build documentation by default. If false, rustdoc and
# friends will still be compiled but they will not be used to generate any
# documentation.
#
# You can still build documentation when this is disabled by explicitly passing paths,
# e.g. `x doc library`.
#docs = true

For me the last line means, that by default the documentation is build. Indeed, ./configure --disable-docs puts in config.toml: docs = false.

• Change the output of ./configure --help from --enable-docs to --disable-docs to indicate what actions users should take in order to deviate from the default behaviour.

See also #129146.