selftests/futex: Conditionally include libnuma support

selftests/futex: Conditionally include libnuma support

Use LIBNUMA_TEST to conditionally add -lnuma to LDLIBS.
Guard numa header includes with #ifdef LIBNUMA_VER_SUFFICIENT
to allow compilation without libnuma installed.

Co-developed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260301-20260128_nylon_chen_sifive_com-v3-1-995ab4cc71aa@sifive.com