stage2 parser: heuristics to pre-allocate token arrays

throughput: 72.2 MiB/s => 75.3 MiB/s

I also tried the idea from the deleted comment in this commit and it
made the throughput worse.
69ff89fd12Andrew Kelley committed on 5/25/2020, 7:12:23 PMparent0ecdbdb
1 file changedLine totals unavailable