libbpf: fix u64-to-pointer cast on 32-bit arches

It's been reported that (void *)map->map_extra is causing compilation
warnings on 32-bit architectures. It's easy enough to fix this by
casting to long first.

Fixes: 79ff13e ("libbpf: Add support for bpf_arena.")
Reported-by: Ryan Eatmon <reatmon@ti.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Message-ID: <20240319215143.1279312-1-andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: anakryiko

tools/lib/bpf/libbpf.c

@@ -5352,8 +5352,8 @@ bpf_object__create_maps(struct bpf_object *obj)
 					goto err_out;
 			}
 			if (map->def.type == BPF_MAP_TYPE_ARENA) {
-				map->mmaped = mmap((void *)map->map_extra, bpf_map_mmap_sz(map),
-						   PROT_READ | PROT_WRITE,
+				map->mmaped = mmap((void *)(long)map->map_extra,
+						   bpf_map_mmap_sz(map), PROT_READ | PROT_WRITE,
 						   map->map_extra ? MAP_SHARED | MAP_FIXED : MAP_SHARED,
 						   map->fd, 0);
 				if (map->mmaped == MAP_FAILED) {