perf: Make perf able to build with latest libbfd

perf: Make perf able to build with latest libbfd

libbfd has changed the bfd_section_* macros to inline functions
bfd_section_<field> since 2019-09-18. See below two commits:
  o http://www.sourceware.org/ml/gdb-cvs/2019-09/msg00064.html
  o https://www.sourceware.org/ml/gdb-cvs/2019-09/msg00072.html

This fix make perf able to build with both old and new libbfd.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200128152938.31413-1-changbin.du@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>