gamemode: use zig build

libs/gamemode/build.zig

@@ -0,0 +1,14 @@
+const std = @import("std");
+
+pub const pkg = std.build.Pkg{
+    .name = "gamemode",
+    .source = .{ .path = thisDir() ++ "/gamemode.zig" },
+};
+
+pub fn link(step: *std.build.LibExeObjStep) void {
+    step.addIncludeDir(comptime thisDir() ++ "/upstream/include");
+}
+
+fn thisDir() []const u8 {
+    return std.fs.path.dirname(@src().file) orelse ".";
+}

libs/gamemode/gamemode.zig

@@ -1,7 +1,7 @@
 //! Note: All the above requests can be blocking - dbus requests can and will block while the daemon
 //! handles the request. It is not recommended to make these calls in performance critical code
 const builtin = @import("builtin");
-pub const c = @import("gamemode_client.zig");
+pub const c = @cImport(@cInclude("gamemode_client.h"));
 
 pub const GamemodeError = error{
     RequestFailed,