prefs: Use threads if available #279

Job	Run time
build-macos	1m 5s
Build on ubuntu-20.04 g++-7	1m 29s
Build on ubuntu-20.04 g++-8	1m 36s
Build on ubuntu20.04 aarch64 g++-8	7m 9s
Build static on ubuntu-latest	1m 25s
Build on ubuntu-latest g++-9	1m 44s
Build on ubuntu20.04 aarch64 g++-9	10m 21s
Build on ubuntu-latest g++-10	54s
Build on ubuntu20.04 aarch64 g++-10	6m 52s
Build on ubuntu-20.04 clang-7	49s
Build on ubuntu22.04 aarch64 g++-12	12m 53s
build-windows	1m 17s
Build on ubuntu-20.04 clang-8	1m 33s
Build on ubuntu20.04 aarch64 clang-9	14m 20s
Build on ubuntu-20.04 clang-9	55s
Build on ubuntu20.04 aarch64 clang-10	19m 56s
Build on ubuntu-20.04 clang-10	51s
Build on ubuntu22.04 aarch64 clang-14	10m 34s
Build on ubuntu-20.04 clang-11	52s
Build on ubuntu22.04 armv7 g++-12	11m 30s
Build on ubuntu-latest clang-12	1m 36s
Build on ubuntu22.04 ppc64le g++-12	9m 18s
Build on ubuntu22.04 s390x g++-12	10m 9s
Build on ubuntu-latest clang-13	1m 45s
Build on ubuntu22.04 riscv64 g++-12	6m 27s
Build on ubuntu-latest clang-14	1m 56s
	2h 19m 16s

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