test/crush: silence warnings from -Walloc-size-larger-than= and -Wstringop-overflow=

test/crush: silence warnings from -Walloc-size-larger-than= and -Wstringop-overflow=

The following warnings appear during make:

/home/jcollin/workspace/ceph/src/test/crush/CrushWrapper.cc: In member function ‘virtual void CrushWrapper_choose_args_compat_Test::TestBody()’:
/home/jcollin/workspace/ceph/src/test/crush/CrushWrapper.cc:1057:20: warning: argument 1 value ‘18446744073709550912’ exceeds maximum object size 9223372036854775807 [-Walloc-size-larger-than=]
   crush_choose_arg choose_args[c.get_max_buckets()];
                    ^~~~~~~~~~~

In function ‘void* memset(void*, int, size_t)’,
    inlined from ‘virtual void CrushWrapper_choose_args_compat_Test::TestBody()’ at /home/jcollin/workspace/ceph/src/test/crush/CrushWrapper.cc:1058:9:
/usr/include/bits/string3.h:90:70: warning: ‘void* __builtin_memset(void*, int, long unsigned int)’: specified size 18446744073709550912 exceeds maximum object size 9223372036854775807 [-Wstringop-overflow=]
   return __builtin___memset_chk (__dest, __ch, __len, __bos0 (__dest));

Signed-off-by: Jos Collin <jcollin@redhat.com>