fix build with compilers with default stack-protector enabled

building systemd fails with a compiler that supports
-fstack-protector but does not enable it by default.
(will miss several __stack_chk_* symbols).

fix this by also adding the switch during linking.

Signed-off-by: Norbert Lange <nolange79@gmail.com>

meson.build

@@ -382,6 +382,7 @@ possible_cc_flags = [
 possible_link_flags = [
         '-Wl,-z,relro',
         '-Wl,-z,now',
+        '-fstack-protector',
 ]
 
 if cc.get_id() == 'clang'