This permits extern function (BTF_KIND_FUNC) be added
to BTF_KIND_DATASEC if a section name is specified.
For example,
-bash-4.4$ cat t.c void foo(int) __attribute__((section(".kernel.funcs"))); int test(void) { foo(5); return 0; }
The extern function foo (BTF_KIND_FUNC) will be put into
BTF_KIND_DATASEC with name ".kernel.funcs".
This will help to differentiate two kinds of external functions,
functions in kernel and functions defined in other bpf programs.
clang-format: please reformat the code