[BPF] print_btf.py: Allow pointer types to have name

Pointer types in Rust have names in LLVM debug info. For example, the
following code, with a struct containing pointer fields:

```rust
    pub struct Foo<'a> {
        a: &'a i32,
    }

    #[unsafe(no_mangle)]
    #[unsafe(link_section = "lsm/file_open")]
    pub fn foo(foo: &Foo) -> i32 {
        let Foo { a } = foo;
        **a
    }
```

Produces the following BTF:

```
    [1] PTR '&rust_btf::Foo' type_id=2
    [2] STRUCT 'Foo' size=8 vlen=1
            'a' type_id=3 bits_offset=0
    [3] PTR '&i32' type_id=4
    [4] INT 'i32' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
    [5] FUNC_PROTO '(anon)' ret_type_id=4 vlen=1
            'foo' type_id=1
    [6] FUNC 'foo' type_id=5 linkage=global
```

Both the pointer type used in the function signature (`&Foo`) and the
one stored in the struct (`&i32`) appear in BTF as named pointer types.

Given that, stop issuing a warning for named pointer types in
`print_btf.py`.

Author: vadorovsky

llvm/test/CodeGen/BPF/BTF/print_btf.py

@@ -160,8 +160,12 @@ def warn_nonzero(val, name):
             warn_nonzero(kflag, "kflag")
             warn_nonzero(vlen, "vlen")
 
+        elif kind == BTF_KIND_PTR:
+            print(f"[{idx}] {kind_name} '{name}' type_id={size}")
+            warn_nonzero(kflag, "kflag")
+            warn_nonzero(vlen, "vlen")
+
         elif kind in [
-            BTF_KIND_PTR,
             BTF_KIND_CONST,
             BTF_KIND_VOLATILE,
             BTF_KIND_RESTRICT,