In D3535, the C++ test suite parts are now run in parallel with each other,
however they all must complete before the (rather long) secp256k1 tests
get started. Thus, little speed benefit was observed.
This queues up the long-running secp256k1 tests in parallel with the start
of the C++ test suite. Some miscellaneous fast tests are left for the end.
This gives a decent speed benefit (~33% less time).
make -j4 check before:
real 2m57.705s user 4m39.254s sys 1m23.918s
make -j4 check after:
real 1m55.976s user 4m38.210s sys 1m23.296s
(old tests pre-D3535: real 3m0.421s)