interpreter: handle multiple dirs in install_emptydir #14510

Job	Run time
Arch Linux	16m 53s
CUDA (on Arch)	5m 33s
Fedora	20m 8s
Arch / PyPy	18m 2s
Ubuntu Rolling (gcc, g++)	15m 36s
OpenSUSE	15m 10s
Ubuntu Bionic	14m 12s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	10m 36s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	10m 49s
Ubuntu Rolling (clang, clang++)	18m 55s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	13m 2s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	10m 32s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	10m 51s
	3h 0m 19s

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