env2mfile: Generalize handling of architecture-prefixed tools on Debian derivatives #16652

Job	Run time
Arch Linux	20m 27s
Arch / PyPy	20m 24s
CUDA (on Arch)	7m 35s
Ubuntu Rolling (gcc, g++)	19m 55s
Fedora	19m 49s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 55s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	14m 7s
Gentoo	21m 53s
Ubuntu Rolling (clang, clang++)	22m 58s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 51s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 44s
OpenSUSE	16m 24s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 32s
Ubuntu Bionic	15m 34s
	3h 56m 8s

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