Use generator expression to get correct OS separator #71

Job	Run time
windows-2019 VS2019	50m 34s
macos-12 appleclang13/C++17 py3.10 MacOS-12	22m 13s
windows-2022 VS2022	52m 9s
Ubuntu latest releases gcc12 C++17 avx2 exr3.2 ocio2.3	17m 37s
macos-13 appleclang14/C++17 py3.11 MacOS-13	29m 56s
VFX2021 gcc9/C++17 py3.7 exr3.1 ocio2.0	13m 57s
macos-14 appleclang15/C++20 py3.11 MacOS-14-ARM	11m 7s
Ubuntu bleeding edge gcc14 C++20 py3.12 OCIO/libtiff/exr-master avx2	7m 35s
VFX2021 clang10/C++17 avx2 exr3.1 ocio2.0	13m 47s
Ubuntu all local builds gcc12 C++17 avx2 exr3.2 ocio2.3	18m 33s
VFX2022 gcc9/C++17 py39 exr3.1 ocio2.1	12m 42s
Ubuntu clang14 C++20 avx2 exr3.1 ocio2.1	13m 28s
VFX2022 clang13/C++17 py39 avx2 exr3.1 ocio2.1	12m 27s
Ubuntu debug gcc9/C++17, sse4.2, exr3.1	17m 45s
VFX2022 icc/C++17 py3.9 exr3.1 ocio2.1 qt5.15	9m 35s
Ubuntu static libs gcc9 C++17 exr2.4	13m 35s
VFX2022 icx/C++17 py3.9 exr3.1 ocio2.2 qt5.15	15m 55s
Ubuntu clang-format	5m 42s
VFX2024 sanitizers	36m 45s
VFX2023 gcc11/C++17 py3.10 exr3.1 ocio2.2	11m 40s
VFX2024 gcc11/C++17 py3.11 exr3.2 ocio2.3	12m 32s
VFX2021 oldest gcc9.3/C++17 py3.7 exr-3.1	16m 17s
VFX2021 hobbled gcc9.3/C++17 py3.7 exr-3.1 no-sse	16m 22s
VFX2023 abi check	12m 0s
	7h 24m 13s

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