glibc: Don't link libpthread stub if all modules are single-threaded

Part of #24347.

Author: alexrp

src/link/Lld.zig

@@ -1217,6 +1217,7 @@ fn elfLink(lld: *Lld, arena: Allocator) !void {
                         if (lib.removed_in) |rem_in| {
                             if (target.os.versionRange().gnuLibCVersion().?.order(rem_in) != .lt) continue;
                         }
+                        if (std.mem.eql(u8, lib.name, "pthread") and !comp.config.any_non_single_threaded) continue;
 
                         const lib_path = try std.fmt.allocPrint(arena, "{}{c}lib{s}.so.{d}", .{
                             comp.glibc_so_files.?.dir_path, fs.path.sep, lib.name, lib.sover,