bpf: Fix BTF_ID symbol generation collision

Marcus and Satya reported an issue where BTF_ID macro generates same
symbol in separate objects and that breaks final vmlinux link.

ld.lld: error: ld-temp.o <inline asm>:14577:1: symbol
'__BTF_ID__struct__cgroup__624' is already defined

This can be triggered under specific configs when __COUNTER__ happens to
be the same for the same symbol in two different translation units,
which is already quite unlikely to happen.

Add __LINE__ number suffix to make BTF_ID symbol more unique, which is
not a complete fix, but it would help for now and meanwhile we can work
on better solution as suggested by Andrii.

Cc: [e-mail]
Reported-by: Satya Durga Srinivasu Prabhala <[e-mail]>
Reported-by: Marcus Seyfarth <[e-mail]>
Closes: https://github.com/ClangBuiltLinux/linux/issues/1913
Debugged-by: Nathan Chancellor <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]/
Signed-off-by: Jiri Olsa <[e-mail]>
Signed-off-by: Nick Desaulniers <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/linux/btf_ids.h

···
 	____BTF_ID(symbol, word)
 
 #define __ID(prefix) \
-	__PASTE(prefix, __COUNTER__)
+	__PASTE(__PASTE(prefix, __COUNTER__), __LINE__)
 
 /*
  * The BTF_ID defines unique symbol for each ID pointing