SLQB: fix compile without optimizations

SLQB fails to build without -O, which causes some external code to trip
over. This BUILD_BUG_ON isn't so useful anyway because it is trivial to
follow that size will be constant, looking at the callers.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

include/linux/slqb_def.h

@@ -237,8 +237,6 @@ static __always_inline struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 {
 	int index;
 
-	BUILD_BUG_ON(!__builtin_constant_p(size));
-
 	index = kmalloc_index(size);
 	if (unlikely(index == 0))
 		return ZERO_SIZE_PTR;