linux

docs: fix another regression in having functional docs #25

Job	Run time
Arch / PyPy	19m 4s
Arch Linux	15m 55s
CUDA (on Arch)	5m 30s
Fedora	20m 10s
OpenSUSE	15m 10s
Ubuntu Bionic	15m 0s
Ubuntu Rolling (gcc, g++)	16m 44s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	10m 40s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	10m 52s
Ubuntu Rolling (clang, clang++)	18m 37s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	12m 48s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	11m 25s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	10m 50s
	3h 2m 45s

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