libbpf: Fix missing #pragma in libbpf_utils.c

The recent sha256 patch uses a GCC pragma to suppress compile errors for
a packed struct, but omits a needed pragma (see related link) and thus
still raises errors: (e.g. on GCC 12.3 armhf)

libbpf_utils.c:153:29: error: packed attribute causes inefficient alignment for ‘__val’ [-Werror=attributes]
  153 | struct __packed_u32 { __u32 __val; } __attribute__((packed));
      |                             ^~~~~

Resolve by adding the GCC diagnostic pragma to ignore "-Wattributes".

Link: https://lore.kernel.org/bpf/CAP-5=fXURWoZu2j6Y8xQy23i7=DfgThq3WC1RkGFBx-4moQKYQ@mail.gmail.com/

Fixes: 4a1c9e5 ("libbpf: remove linux/unaligned.h dependency for libbpf_sha256()")
Signed-off-by: Tony Ambardar <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: guidosarducci

tools/lib/bpf/libbpf_utils.c

@@ -150,6 +150,7 @@ const char *libbpf_errstr(int err)
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wpacked"
+#pragma GCC diagnostic ignored "-Wattributes"
 struct __packed_u32 { __u32 __val; } __attribute__((packed));
 #pragma GCC diagnostic pop