configury: add support for x32 architecture

Thanks Alastair McKinstry for the patch

Fixes open-mpi/ompi#2515

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

config/opal_config_asm.m4

@@ -1003,6 +1003,11 @@ AC_DEFUN([OPAL_CONFIG_ASM],[
         OPAL_GCC_INLINE_ASSIGN=""
         OPAL_ASM_SUPPORT_64BIT=0
         case "${host}" in
+        x86_64-*x32)
+            opal_cv_asm_arch="AMD64"
+            OPAL_ASM_SUPPORT_64BIT=1
+            OPAL_GCC_INLINE_ASSIGN='"xaddl %1,%0" : "=m"(ret), "+r"(negone) : "m"(ret)'
+            ;;
         i?86-*|x86_64*)
             if test "$ac_cv_sizeof_long" = "4" ; then
                 opal_cv_asm_arch="IA32"