MDEV-28836 fixup

On GNU/Linux, even though the C11 aligned_alloc() appeared in
GNU libc early on, some custom memory allocators did not
implement it until recently. For example, before
gperftools/gperftools@d406f22853
the free() in tcmalloc would fail to free memory that was
returned by aligned_alloc(), because the latter would map to the
built-in allocator of libc. The Linux specific memalign() has a
similar interface and is safer to use, because it has been
available for a longer time. For AddressSanitizer, we will use
aligned_alloc() so that the constraint on size can be enforced.

buf_tmp_reserve_compression_buf(): When HAVE_ALIGNED_ALLOC holds,
round up the size to be an integer multiple of the alignment.

pfs_malloc(): In the unit test stub, round up the size to be an
integer multiple of the alignment.

include/aligned.h

@@ -14,12 +14,19 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1335  USA */
 
+#ifdef HAVE_ALIGNED_ALLOC
+#elif defined __linux__
+# include <malloc.h>
+#endif
+
 inline void *aligned_malloc(size_t size, size_t alignment)
 {
 #ifdef _WIN32
   return _aligned_malloc(size, alignment);
 #elif defined HAVE_ALIGNED_ALLOC
   return aligned_alloc(alignment, size);
+#elif defined __linux__
+  return memalign(alignment, size);
 #else
   void *result;
   if (posix_memalign(&result, alignment, size))