depfixer: fix rpath iterating on chars #15800

Job	Run time
Arch / PyPy	20m 12s
Arch Linux	19m 6s
CUDA (on Arch)	7m 54s
Fedora	19m 56s
Ubuntu Rolling (gcc, g++)	15m 46s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	11m 21s
Gentoo	21m 9s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	11m 37s
OpenSUSE	15m 26s
Ubuntu Rolling (clang, clang++)	19m 17s
Ubuntu Bionic	14m 31s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	13m 24s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	11m 39s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	10m 44s
	3h 32m 2s

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