Merge pull request #1657 from bgoglin/hwloc-for-2.0

configure: check the actual may_alias syntax that we use

opal/mca/hwloc/hwloc1112/hwloc/README-ompi.txt

@@ -2,3 +2,4 @@ Cherry-picked commits after 1.11.2:
 
 open-mpi/hwloc@d2d07b9a2268699e13e1644b4f2ef7a53ef7396c
 open-mpi/hwloc@9549fd59af04dca2e2340e17f0e685f8c552d818
+open-mpi/hwloc@0ab7af5e90fc2b58be30b2126cc2a73f9f7ecfe9

opal/mca/hwloc/hwloc1112/hwloc/config/hwloc_check_attributes.m4

@@ -322,9 +322,10 @@ AC_DEFUN([_HWLOC_CHECK_ATTRIBUTES], [
     # Attribute may_alias: No suitable cross-check available, that works for non-supporting compilers
     # Ignored by intel-9.1.045 -- turn off with -wd1292
     # Ignored by PGI-6.2.5; ignore not detected due to missing cross-check
+    # The test case is chosen to match our only use in topology-xml-*.c, and reproduces an xlc-13.1.0 bug.
     #
     _HWLOC_CHECK_SPECIFIC_ATTRIBUTE([may_alias],
-        [int * p_value __attribute__ ((__may_alias__));],
+        [struct { int i; } __attribute__ ((__may_alias__)) * p_value;],
         [],
         [])