meson: enable stack protector on freebsd and windows

Fedora 33 rawhide no longer successfully builds GTK-VNC on mingw using
fortify source, without also having stack protector flags enabled/
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

meson.build

@@ -231,12 +231,6 @@ check_cflags = [
   '-Wno-suggest-attribute=pure',
   '-Wno-suggest-attribute=const',
 ]
-if host_machine.system() == 'linux'
-  check_cflags += [
-    '-fstack-protector-all',
-    '--param=ssp-buffer-size=4',
-  ]
-endif
 
 cflags = []
 foreach cflag: check_cflags
@@ -246,6 +240,21 @@ foreach cflag: check_cflags
 endforeach
 
 
+if host_machine.system() in [ 'linux', 'freebsd', 'windows' ]
+  # we prefer -fstack-protector-strong but fallback to -fstack-protector-all
+  fstack_cflags = cc.first_supported_argument([
+    '-fstack-protector-strong',
+    '-fstack-protector-all',
+  ])
+  cflags += fstack_cflags
+
+  # When building with mingw using -fstack-protector requires libssp library
+  # which is included by using -fstack-protector with linker.
+  if fstack_cflags.length() == 1 and host_machine.system() == 'windows'
+    add_project_link_arguments(fstack_cflags, language: 'c')
+  endif
+endif
+
 add_project_arguments(cflags, language: 'c')
 
 gtk_vnc_prefix = get_option('prefix')