pthread: fix key destructor calling and start function exit #931

All 5 316 tests pass, 641 skipped in 29m 9s

5 957 tests +8 5 316 ✔️ +20 29m 9s ⏱️ +13s
  333 suites +8   641 💤 - 12
      1 files ±0       0 ❌ ±  0

Results for commit 47c37cb. ± Comparison against earlier commit 87e41cb.