For Travis CI - Revert back to always install ALSA for all platforms.
Straightly speaking ALSA is not required while cross-compiling to other non-Linux targets. However, in the CI build we have enabled Lua or LuaJIT and because of that we have to build some native tool(s). The problem is when configuring native project on a Linux build system, we could not inform our CMake script to ONLY configure for the tool building. Currently the script always attempt to configure most of things including SDL which in turns depends on ALSA, although actually the Lua tool building does not require it.
[ci package]