希望加入LoongArch（loong64）架构支持 / Request for loong64 support

[Moooebie]

您好！
我使用的平台是龙芯3A6000（新世界，Arch Linux），直接使用编译脚本会在最后一步linking时报错，检查后发现是因为仓库里预编译的ffmpeg只有x86和arm64。手动将预编译的ffmpeg和adb替换为loong64版本后，成功构建并运行，且功能一切正常。
希望作者可以加入loong64架构的预编译依赖；或者说干脆预留一个flag用来直接使用系统里的ffmpeg库或者从源码编译，这样就能兼顾所有其他架构了。

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Hello. I am using a Loongson 3A6000 CPU (running "new world" distro Arch Linux). Attempt to build the project by running the given build script has failed, due to prebuilt dependencies only have x86 and arm64 variants. By replacing the prebuilt ffmpeg and adb with loong64 variants, the project built successfully and all functions were working.
I hope that the project would include loong64 variants for the dependencies so it would support this architecture; alternatively, a flag could be added to allow finding dependencies from the shared libs in the OS or build them from the source rather than using the prebuilt blobs, so that the project could be more easily ported to other CPU architectures.