Resolve (some of) parallelism bottlenecks in test suites

[Xi Ruoyao]

There are some parallelism bottlenecks in test suites:

• Autoconf, Libtool, Tar, and maybe others
  • Solution: set TESTSUITEFLAGS=-j$N globally (like MAKEFLAGS)
• Automake (with more than 4 cores)
  • Solution: set -j $(($N > 4 ? $N : 4)) instead of just -j4
• OpenSSL
  • Solution: HARNESS_JOBS=$N make test
• Perl
  • Solution: TEST_JOBS=$N make test_harness
• Binutils and Libffi
  • Not solvable, limitation of DejaGNU. GCC has managed to resolve the issue but the solution is very complex.