eealloc, pagealign_alloc, xalloc: avoid clang warnings Avoid [-Wunknown-attributes] warnings like: warning: unknown attribute '__alloc_size__' ignored * lib/xalloc.h: Don't use the __alloc_size__ attribute with clang, as support has been fully removed as of clang 3.5: https://github.com/llvm-mirror/clang/commit/c047507a * lib/eealloc.h: Likewise. * lib/pagealign_alloc.h: Likewise.