Detect duplicate backend worker thread on windows #49

Job	Run time
build (g++-8, Debug, 17, ubuntu-22.04, ON)	2m 12s
build (g++-8, Release, 17, ubuntu-22.04, ON)	2m 56s
build (g++-10, Debug, 17, ubuntu-22.04, ON)	2m 5s
build (g++-10, Release, 17, ubuntu-22.04, ON)	3m 0s
build (g++-13, Release, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	3m 55s
build (g++-13, Debug, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	3m 38s
build (g++-10, Release, 17, ubuntu-22.04, OFF, -DQUILL_NO_EXCEPTIONS=ON)	2m 4s
build (g++-10, Release, 20, ubuntu-22.04, ON, -DQUILL_USE_VALGRIND=ON, -T memcheck, sudo apt -o A...	3m 50s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_ADDRESS=ON)	7m 11s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_THREAD=ON)	4m 45s
build (clang++-19, Release, 17, ubuntu-22.04, ON, wget -O - https://apt.llvm.org/llvm-snapshot.gp...	3m 27s
	39m 3s

Provide feedback