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

Based on 8a7dcd4ef1a3f99f15fa27eab60885cef377c4a5.

Bring back winpthreads originally removed in vlc-debian-llvm-mingw.
1 job for master in 32 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #496525
build

00:32:05

 
Name Stage Failure
failed
build Build
 ( cd '/opt/llvm-mingw/aarch64-w64-mingw32/lib' && aarch64-w64-mingw32-ranlib libmoldname.a )
( cd '/opt/llvm-mingw/aarch64-w64-mingw32/lib' && aarch64-w64-mingw32-ranlib libmingwthrd.a )
( cd '/opt/llvm-mingw/aarch64-w64-mingw32/lib' && aarch64-w64-mingw32-ranlib libucrtbase.a )
make[2]: Leaving directory '/build/mingw-w64/mingw-w64-crt/build-aarch64'
make[1]: Leaving directory '/build/mingw-w64/mingw-w64-crt/build-aarch64'
/bin/sh: 1: ./build-mingw-w64-tools.sh: Permission denied
The command '/bin/sh -c ./build-llvm.sh $TOOLCHAIN_PREFIX && ./strip-llvm.sh $TOOLCHAIN_PREFIX && ./install-wrappers.sh $TOOLCHAIN_PREFIX && MINGW_W64_VERSION=ecb4ff5498dfedd6abcbadb889b84fab19ee57b2 ./build-mingw-w64.sh $TOOLCHAIN_PREFIX --with-default-msvcrt=$DEFAULT_CRT --with-default-win32-winnt=0xA00 && ./build-mingw-w64-tools.sh $TOOLCHAIN_PREFIX && ./build-compiler-rt.sh $TOOLCHAIN_PREFIX && ./build-mingw-w64-libraries.sh $TOOLCHAIN_PREFIX && ./build-libcxx.sh $TOOLCHAIN_PREFIX && ./build-compiler-rt.sh $TOOLCHAIN_PREFIX --build-sanitizers && rm -rf /build/*' returned a non-zero code: 126
Cleaning up file based variables
ERROR: Job failed: exit code 126