The known keywords for each function are obtained by scraping the
documentation for lines matching a particular regular expression. In
commit 8842a027 (ExternalProject: Improve documentation, 2017-07-09),
the docs were overhauled and the COMMAND docs subsequently matched the
regular expression when they shouldn't have. This made COMMAND appear as
a true keyword, which thwarted the special handling logic elsewhere for
the intended use of COMMAND arguments.

This commit contains a workaround for issue #17229 to force a dependency
of the patch step on the update step to ensure a predictable step order.

Fixes: #17198