Merge topic 'sphinx-linkcheck'

a89c76a773 Build: Add `SPHINX_LINKCHECK` build option
137b00cda1 Build: Do not redirect `sphinx-build` output if CMake running in verbose mode
d954fb8a60 Build: Deduplicate `add_custom_command()` calls for Sphinx targets
2af8724485 Merge branch 'backport-sphinx-linkcheck' into sphinx-linkcheck
435b0c573c Help: Fix some redirects reported with sphinx linkcheck
ac5295a9de Help: Fix broken external links found by sphinx linkcheck

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !7876