rcache: Handle posix_memalign failures

Glibc tags posix_memalign to generate a warning if the return value
is ignored.  In recent systems, this seems completely uncalled for,
since addr must not be touched.  But older systems did not enforce
that behavior, so reset addr and move on.

Signed-off-by: Brian Barrett <bbarrett@amazon.com>

Author: bwbarrett

opal/mca/mpool/base/mpool_base_default.c

@@ -34,7 +34,12 @@ static void *mca_mpool_default_alloc(mca_mpool_base_module_t *mpool, size_t size
     if (align <= sizeof(void *)) {
         addr = malloc(size);
     } else {
-        (void) posix_memalign(&addr, align, size);
+        int ret = posix_memalign(&addr, align, size);
+        if (ret < 0) {
+            /* old systems may not guarantee that addr wasn't modified
+               on failure */
+            addr = NULL;
+        }
     }
     return addr;
 #else