checkdeclares: find struct declared more than once.  Inspired by
checkincludes.pl.

This script checks for duplicate struct declares.  Note that this will not
take into consideration macros, so you should run this only if you know
you do have real dups and do not have them under #ifdef's.  You could also
just review the results.

[akpm@linux-foundation.org: fix usage message, grammar]

Link: https://lkml.kernel.org/r/20210401110943.1010796-1-wanjiabing@vivo.comSigned-off-by: Wan Jiabing <wanjiabing@vivo.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>