Fix amd64 build on FreeBSD


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4020 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/common/jpeg/acinclude.m4 b/common/jpeg/acinclude.m4
index b8254b6..570e606 100644
--- a/common/jpeg/acinclude.m4
+++ b/common/jpeg/acinclude.m4
@@ -44,7 +44,14 @@
     if echo __ELF__ | $CC -E - | grep __ELF__ > /dev/null; then
       objfmt='BSD-a.out'
     else
-      objfmt='ELF'
+      case "$host_cpu" in
+        x86_64)
+          objfmt='ELF64'
+          ;;
+        *)
+          objfmt='ELF'
+          ;;
+      esac
     fi
   ;;
   solaris* | sunos* | sysv* | sco*)