Don't require RELRO and BIND_NOW for Darwin

Xcode's ld (at least ld64-302.3) doesn't support -z

configure.ac

@@ -489,8 +489,14 @@ if test x$use_hardening != xno; then
     HARDENED_CPPFLAGS="$HARDENED_CPPFLAGS -D_FORTIFY_SOURCE=2"
   ],[AC_MSG_ERROR(Cannot enable -D_FORTIFY_SOURCE=2)])
 
-  AX_CHECK_LINK_FLAG([[-Wl,-z,relro]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,relro"],[AC_MSG_ERROR(Cannot enable RELRO)])
-  AX_CHECK_LINK_FLAG([[-Wl,-z,now]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,now"],[AC_MSG_ERROR(Cannot enable BIND_NOW)])
+  if test x$BUILD_OS = xdarwin; then
+    # Xcode's ld (at least ld64-302.3) doesn't support -z
+    AX_CHECK_LINK_FLAG([[-Wl,-z,relro]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,relro"],[AC_MSG_WARN(Cannot enable RELRO)])
+    AX_CHECK_LINK_FLAG([[-Wl,-z,now]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,now"],[AC_MSG_WARN(Cannot enable BIND_NOW)])
+  else
+    AX_CHECK_LINK_FLAG([[-Wl,-z,relro]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,relro"],[AC_MSG_ERROR(Cannot enable RELRO)])
+    AX_CHECK_LINK_FLAG([[-Wl,-z,now]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,now"],[AC_MSG_ERROR(Cannot enable BIND_NOW)])
+  fi
 
   if test x$TARGET_OS != xwindows; then
     # All windows code is PIC, forcing it on just adds useless compile warnings