Update mca_mpool_base_alloc to use malloc instead of posix_memalign for alignment requests of <= sizeof(void *). This works around issue #4564.

Signed-off-by: Ben Menadue <ben.menadue@nci.org.au>

opal/mca/mpool/base/mpool_base_default.c

@@ -31,7 +31,11 @@ static void *mca_mpool_default_alloc (mca_mpool_base_module_t *mpool, size_t siz
 #if HAVE_POSIX_MEMALIGN
     void *addr = NULL;
 
-    (void) posix_memalign (&addr, align, size);
+    if (align <= sizeof(void *)) {
+        addr = malloc (size);
+    } else {
+        (void) posix_memalign (&addr, align, size);
+    }
     return addr;
 #else
     void *addr, *ret;