bpf: Replace __diag_ignore with unified __diag_ignore_all

Currently, -Wmissing-prototypes warning is ignored for GCC, but not
clang. This leads to clang build warning in W=1 mode. Since the flag
used by both compilers is same, we can use the unified __diag_ignore_all
macro that works for all supported versions and compilers which have
__diag macro support (currently GCC >= 8.0, and Clang >= 11.0).

Also add nf_conntrack_bpf.h include to prevent missing prototype warning
for register_nf_conntrack_bpf.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220304224645.3677453-8-memxor@gmail.com

net/bpf/test_run.c

@@ -201,7 +201,7 @@ static int bpf_test_finish(const union bpf_attr *kattr,
  * future.
  */
 __diag_push();
-__diag_ignore(GCC, 8, "-Wmissing-prototypes",
+__diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
 int noinline bpf_fentry_test1(int a)
 {

net/netfilter/nf_conntrack_bpf.c

@@ -12,6 +12,7 @@
 #include <linux/btf_ids.h>
 #include <linux/net_namespace.h>
 #include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_bpf.h>
 #include <net/netfilter/nf_conntrack_core.h>
 
 /* bpf_ct_opts - Options for CT lookup helpers
@@ -102,7 +103,7 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net,
 }
 
 __diag_push();
-__diag_ignore(GCC, 8, "-Wmissing-prototypes",
+__diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in nf_conntrack BTF");
 
 /* bpf_xdp_ct_lookup - Lookup CT entry for the given tuple, and acquire a