Add build support for s390x #34

Job	Run time
linux-cmake	1m 18s
linux-autotools	1m 35s
macos-autotools	1m 33s
macos-cmake	1m 44s
linux-sanitizers-gcc-autotools	2m 49s
linux-sanitizers-clang-cmake	2m 16s
mingw-cross-autotools	1m 17s
msys-cmake	4m 57s
linux-ffmpeg	5m 19s
llvm-mingw	1m 3s
mingw-cross-cmake	1m 18s
msvc-cmake	58s
msvc-cmake-arm64	1m 25s
msvc-cmake-ninja-arm	1m 15s
	28m 47s

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