failed assertion after e372a5f

Simon,
idk if you have your email notifications from github turned off, but
there's at least two reports on e372a5f about failed assertions;
please address:
https://github.com/llvm/llvm-project/commit/e372a5f86f6488bb0c2593a665d51fdd3a97c6e4#commitcomment-43425310

This should have been fixed by the reversions by @mstorsjo finishing at rG4de215ff1877

I'm sorry about this - I've been having a few problems both with email and the new buildbot webview isn't refreshing properly for me so it hasn't been easy to see when one of my commits has caused reds.

No worries, thanks! (I'll confirm the fix later)