[llvm] [InstrRef][nfc] Remove usage of unique_ptrs of arrays (PR #74203)

[Nikita Popov via llvm-commits]

nikic wrote:

You need to pass `--trace-children=yes` to valgrind to follow fork.

I just tested this myself locally, and I can reproduce the difference. The `time` output is 158696 before and 171124 after.

Here are the massif results for the two runs: https://gist.github.com/nikic/bfdd7686c0d6c1ddc076d527148da851 These show a peak of 72MB vs 84MB.

https://github.com/llvm/llvm-project/pull/74203