[PATCH] Support 'exclude' in objcopy --set-section-flags

[Fangrui Song]

On 2020-01-16, Fangrui Song via binutils wrote:
>https://sourceware.org/bugzilla/show_bug.cgi?id=25371
>
>commit 18ae9cc1db45e2e7f6467b91d8abbc5eb45fbaa5 makes SHF_EXCLUDE
>generic, not like other SHF_MASKPROC flags. So we do not preserve
>SHF_EXCLUDE when setting sh_flags.
>
>--set-section-flags .foo= => clear SHF_EXCLUDE
>--set-section-flags .foo=exclude => set SHF_EXCLUDE

Ping :)