staging: lustre: remove CLASSERT macro

lustre uses a fake switch() statement as a compile-time assert, but unfortunately
each use of that causes a warning when building with clang:

drivers/staging/lustre/lnet/klnds/socklnd/socklnd.c:2907:2: warning: no case matching constant switch condition '42'
drivers/staging/lustre/lnet/klnds/socklnd/../../../include/linux/libcfs/libcfs_private.h:294:36: note: expanded from macro 'CLASSERT'
 #define CLASSERT(cond) do {switch (42) {case (cond): case 0: break; } } while (0)

As Greg suggested, let's just kill off this macro completely instead of
fixing it. This replaces it with BUILD_BUG_ON(), which means we have
to negate all the conditions in the process.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>