Emscripten build with sokol-zig and Ziglua

[luchak]

This is mostly a combination thank you and FYI, prompted by a probably-niche use case - not asking for anything! I've been trying to figure out how to integrate Lua into my project and still keep the web build working. Because of libc++ problems (Luau) and longjmp issues (Lua 5.x), the only way I could find to get the whole thing working was to compile and link Lua explicitly with a single version of emsdk: https://github.com/natecraddock/ziglua/pull/95/files . I used sokol-zig's link step and added a similar compile step helper.

I had a problem with my Github CD pipeline where the two emsdk setup steps were stomping on each other, so I had to add the possibly-questionable line:

dep_ziglua.artifact("luau").step.dependOn(&dep_sokol.artifact("sokol_clib").step);

into my build.zig - otherwise things seem to be working fine now.