tools/sched_ext: Add -fms-extensions to bpf build flags

Similar to commit 835a5075 ("selftests/bpf: Add -fms-extensions to
bpf build flags") and commit 639f58a0 ("bpftool: Fix build warnings
due to MS extensions")

The kernel is now built with -fms-extensions, therefore
generated vmlinux.h contains types like:
struct aes_key {
        struct aes_enckey;
        union aes_invkey_arch inv_k;
};

struct ns_common {
	...
        union {
                struct ns_tree;
                struct callback_head ns_rcu;
        };
};

Which raise warning like below when building scx scheduler:

tools/sched_ext/build/include/vmlinux.h:50533:3: warning:
declaration does not declare anything [-Wmissing-declarations]
 50533 |                 struct ns_tree;
       |                 ^
Fix it by using -fms-extensions and -Wno-microsoft-anon-tag flags
to build bpf programs that #include "vmlinux.h"

Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>