Add build support for s390x #33

Job	Run time
linux-sanitizers-gcc-autotools	3m 4s
linux-cmake	1m 16s
linux-autotools	1m 29s
macos-autotools	1m 40s
macos-cmake	1m 29s
mingw-cross-autotools	1m 22s
mingw-cross-cmake	1m 27s
linux-ffmpeg	6m 8s
linux-sanitizers-clang-cmake	2m 41s
llvm-mingw	1m 4s
msvc-cmake	2m 2s
msvc-cmake-arm64	1m 53s
msvc-cmake-ninja-arm	1m 46s
msys-cmake	5m 0s
	32m 21s

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