Every American and British government has both backed the Saudis and armed it. This goes back to 1932 when Saudi Arabia was created. That means that five Labour governments have backed and armed Saudi Arabia since 1932.
What about the many other repressive Muslim states, such as Pakistan (which, in many ways, is worse than Saudi Arabia), Malaysia, Indonesia, Turkey, Egypt, Sudan, Lebanon, etc.? Will Corbyn stop arming all of these? Of course not! Will he stop funding any of them? It's hard to say.