Currently the rust docs are generated for each entry of SPHINXDIRS,
even those not mentioning the rust directory.

Only generate the rust docs only once and only when requested.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Thomas Weißschuh (4):
      tools/docs: sphinx-build-wrapper: generate rust docs only once
      tools/docs: sphinx-build-wrapper: make 'rustdoc' a local variable
      tools/docs: sphinx-build-wrapper: compute sphinxdirs_list earlier
      tools/docs: sphinx-build-wrapper: only generate rust docs when requested

 tools/docs/sphinx-build-wrapper | 80 +++++++++++++++++++++--------------------
 1 file changed, 41 insertions(+), 39 deletions(-)
---
base-commit: e1a8301cd941b8029893500e6857d7978873483f
change-id: 20260117-docs-spurious-rust-8ffa2748925c

Best regards,
-- 
Thomas Weißschuh [off-list ref]