build: Fix platform detection on FreeBSD

Look for amd64 in addition to x86_64 as the platform
type for x86_64 assembly.  The FreeBSD-packaged
Autoconf package has a patch to return
amd64-unknown-freebsd11.0 instead of the
x86_64-unknown-freebsd11.0 that a stock Autoconf
package would return.  Since we want to run Jenkins
builds on FreeBSD, working around the FreeBSD patch
is probably the easiest thing.

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

LICENSE

@@ -53,6 +53,8 @@ Copyright (c) 2014-2015 Hewlett-Packard Development Company, LP.  All
                         rights reserved.
 Copyright (c) 2013-2017 Research Organization for Information Science (RIST).
                         All rights reserved.
+Copyright (c) 2017      Amazon.com, Inc. or its affiliates.  All Rights
+                        reserved.
 
 $COPYRIGHT$
 

config/opal_config_asm.m4

@@ -15,6 +15,8 @@ dnl Copyright (c) 2015-2017 Research Organization for Information Science
 dnl                         and Technology (RIST). All rights reserved.
 dnl Copyright (c) 2014-2016 Los Alamos National Security, LLC. All rights
 dnl                         reserved.
+dnl Copyright (c) 2017      Amazon.com, Inc. or its affiliates.  All Rights
+dnl                         reserved.
 dnl $COPYRIGHT$
 dnl
 dnl Additional copyrights may follow
@@ -1000,7 +1002,7 @@ AC_DEFUN([OPAL_CONFIG_ASM],[
             OPAL_ASM_SUPPORT_64BIT=1
             OPAL_GCC_INLINE_ASSIGN='"xaddl %1,%0" : "=m"(ret), "+r"(negone) : "m"(ret)'
             ;;
-        i?86-*|x86_64*)
+        i?86-*|x86_64*|amd64*)
             if test "$ac_cv_sizeof_long" = "4" ; then
                 opal_cv_asm_arch="IA32"
             else