Add support for .hg_archival.txt to detect_vcs #17436

Job	Run time
Arch / PyPy	20m 8s
Ubuntu Rolling (gcc, g++)	19m 45s
Arch Linux	20m 10s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 30s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	14m 11s
Ubuntu Rolling (clang, clang++)	22m 33s
CUDA (on Arch)	6m 59s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 46s
Fedora	17m 41s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 5s
Gentoo	23m 6s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 49s
OpenSUSE	16m 39s
Ubuntu Bionic	15m 17s
	3h 52m 39s

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