xwayland: Fix build without <sys/random.h>

The include <sys/random.h> was added to glibc-2.25, previously was
<linux/random.h>.

Adjust meson build and code to accomodate both.

Fixes: a8984a81c "xwayland: Generate a Xauth file and pass this to
                  Xwayland when starting it"

https://gitlab.gnome.org/GNOME/mutter/merge_requests/633

config.h.meson

@@ -61,5 +61,6 @@
 /* XKB base prefix */
 #mesondefine XKB_BASE
 
-/* Default rules for allowing Xwayland grabs */
-#mesondefine XWAYLAND_GRAB_DEFAULT_ACCESS_RULES
+/* Either <sys/random.h> or <linux/random.h> */
+#mesondefine HAVE_SYS_RANDOM
+#mesondefine HAVE_LINUX_RANDOM

meson.build

@@ -364,6 +364,15 @@ if have_wayland
     xwayland_path = find_program('Xwayland').path()
   endif
   cdata.set_quoted('XWAYLAND_PATH', xwayland_path)
+
+  # For Xwayland authority file generation.
+  if cc.has_header_symbol('sys/random.h', 'getrandom')
+    cdata.set('HAVE_SYS_RANDOM', 1)
+  elif cc.has_header_symbol('linux/random.h', 'getrandom')
+    cdata.set('HAVE_LINUX_RANDOM', 1)
+  else
+    error('Required function getrandom not found')
+  endif
 endif
 
 xwayland_grab_default_access_rules = get_option('xwayland_grab_default_access_rules')

src/wayland/meta-xwayland.c

@@ -31,7 +31,11 @@
 #include <glib.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#if defined(HAVE_SYS_RANDOM)
 #include <sys/random.h>
+#elif defined(HAVE_LINUX_RANDOM)
+#include <linux/random.h>
+#endif
 #include <unistd.h>
 #include <X11/Xauth.h>