alignalloc: work around AddressSanitizer bug * doc/posix-functions/aligned_alloc.texi (aligned_alloc): Mention AddressSanitizer bug. * lib/alignalloc.h (ALIGNALLOC_VIA_ALIGNED_ALLOC): Define to 0 if AddressSanitizer is in use. * tests/test-alignalloc.c (test_alignalloc): New function, which tests for non-aligned sizes too. (main): Use it. Don’t bother checking for alignments greater than 16 MiB, as this flummoxes AddressSanitizer and there seems little point to testing them.