Merge branch 'typedef-func_proto'

Merge branch 'typedef-func_proto'

Yonghong Song says:

====================
The current btf implementation disallows the typedef of
a func_proto type. This actually is allowed per C standard.
This patch fixed btf verification to permit such types.
Patch #1 fixed the kernel side and Patch #2 fixed
the tools test_btf test.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>