vlc-debian-llvm-mingw: bring closer to llvm-mingw

Based on 8a7dcd4ef1a3f99f15fa27eab60885cef377c4a5.

Bring back winpthreads removed in b37e0bdd
1 job for master in 43 minutes and 38 seconds (queued for 2 seconds)
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passed #496605
build

00:43:38