Parallelize src/test/test into chunks.
First, we introduce a flag to teach src/test/test to split its work into chunks. Then we replace our invocation of src/test/test in our "make check" target with a set of 8 scripts that invoke the first 8th of the tests, the second 8th, and so on. This change makes our "make -kj4 check" target in our hardened gitlab build more than twice as fast, since src/test/test was taking the longest to finish. Closes 40098.
parallel_test_035 in 27 minutes and 23 seconds (queued for 10 minutes and 21 seconds)5 jobs for