libbpf, selftests/bpf: Adjust libbpf, bpftool, selftests to match LLVM

The selftests use
to tell LLVM about special pointers. For LLVM there is nothing "arena"
about them. They are simply pointers in a different address space.
Hence LLVM diff llvm/llvm-project#85161 renamed:
. macro __BPF_FEATURE_ARENA_CAST -> __BPF_FEATURE_ADDR_SPACE_CAST
. global variables in __attribute__((address_space(N))) are now
  placed in section named ".addr_space.N" instead of ".arena.N".

Adjust libbpf, bpftool, and selftests to match LLVM.

Signed-off-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Stanislav Fomichev <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: Alexei Starovoitov

src/libbpf.c

@@ -498,7 +498,7 @@ struct bpf_struct_ops {
 #define KSYMS_SEC ".ksyms"
 #define STRUCT_OPS_SEC ".struct_ops"
 #define STRUCT_OPS_LINK_SEC ".struct_ops.link"
-#define ARENA_SEC ".arena.1"
+#define ARENA_SEC ".addr_space.1"
 
 enum libbpf_map_type {
 	LIBBPF_MAP_UNSPEC,