Candidate patch for 3.3.1

[Tim Northover]

Hi Tom,

Rather late, but I've just remembered that r182190 (a fix in AArch64
for parallel builds) is a good candidate for the point release. It's
just a CMake change so that deps are built before their uses.

Could I commit it to release_33 (or whatever it is)? And if so, should
I do it as a merge commit or follow any other special procedure?

Cheers.

Tim.