libbpf: define __uptr.

Make __uptr available to BPF programs to enable them to define uptrs.

Acked-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Kui-Feng Lee <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/lib/bpf/bpf_helpers.h

···
 #define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))
 #define __kptr __attribute__((btf_type_tag("kptr")))
 #define __percpu_kptr __attribute__((btf_type_tag("percpu_kptr")))
+#define __uptr __attribute__((btf_type_tag("uptr")))
 
 #if defined (__clang__)
 #define bpf_ksym_exists(sym) ({						\