Add ARM Linux build config. #16

Job	Run time
Build (ubuntu-latest, aarch64-pc-windows-gnullvm, curl -L -O https://github.com/mstorsjo/llvm-min...	40s
Build (ubuntu-latest, i686-unknown-linux-gnu, sudo apt update && sudo apt install -y gcc-multilib...	1m 26s
Build (macOS-latest, aarch64-apple-darwin, -DCMAKE_OSX_ARCHITECTURES=arm64, macos/arm64)	29s
Build (windows-2019, x86_64-pc-windows-msvc, cmd.exe /k "C:\Program Files (x86)\Microsoft Visual ...	3m 14s
Build (ubuntu-latest, x86_64-pc-windows-gnullvm, curl -L -O https://github.com/mstorsjo/llvm-ming...	45s
Build (ubuntu-latest, i686-pc-windows-gnullvm, curl -L -O https://github.com/mstorsjo/llvm-mingw/...	43s
Build (ubuntu-latest, x86_64-unknown-linux-gnu, linux/x86_64)	1m 13s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, curl -L -O https://github.com/godotengine/buildr...	1m 35s
Build (windows-2019, aarch64-pc-windows-msvc, cmd.exe /k "C:\Program Files (x86)\Microsoft Visual...	2m 17s
Build (windows-2019, i686-pc-windows-msvc, cmd.exe /k "C:\Program Files (x86)\Microsoft Visual St...	2m 6s
Build (macOS-latest, x86_64-apple-darwin, -DCMAKE_OSX_ARCHITECTURES=x86_64, macos/x86_64)	33s
Build (ubuntu-latest, x86_64-pc-windows-gnu, sudo apt update && sudo apt install -y mingw-w64, -D...	2m 7s
Build (ubuntu-latest, i686-pc-windows-gnu, sudo apt update && sudo apt install -y mingw-w64, -DCM...	2m 24s
Build (ubuntu-latest, arm-unknown-linux-gnueabihf, curl -L -O https://github.com/godotengine/buil...	1m 40s
	21m 12s

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