minimal build.zig for wasm, January 2024, zig version 0.12.0-dev.2158+4f2009de1

build.zig

const std = @import("std");

pub fn build(b: *std.Build) void {
    const optimize = b.standardOptimizeOption(.{});
    const exe = b.addExecutable(.{
        .name = "lib",
        .root_source_file = .{ .path = "src/lib.zig" },
        .target = b.resolveTargetQuery(std.zig.CrossTarget.parse(
            .{ .arch_os_abi = "wasm32-freestanding" },
        ) catch unreachable),
        .optimize = optimize,
    });
    exe.entry = .disabled;
    exe.rdynamic = true;
    b.installArtifact(exe);
}