[Wayland] Use read-only anonymous file abstraction for wayland-keymap sharing

Add ro_anonymous_file, an abstraction around anonymous read-only files.
Files can be created by calling os_ro_anonymous_file_create(), passing
the data of the file. Subsequent calls to os_ro_anonymous_file_get_fd()
return a fd that's ready to be send over the socket.
Use this new abstraction in meta-wayland-keyboard for sending keymap data to the clients without having to copy it unnecessarily.

Author: Sunderland93

cogl/tests/conform/mutter-cogl.test.in cogl/tests/conform/muffin-cogl.test.incogl/tests/conform/mutter-cogl.test.in renamed to cogl/tests/conform/muffin-cogl.test.in

@@ -76,3 +76,12 @@
 
 /* Whether the Xwayland supports +/-byteswappedclients */
 #mesondefine HAVE_XWAYLAND_BYTE_SWAPPED_CLIENTS
+
+/* Whether the mkostemp function exists */
+#mesondefine HAVE_MKOSTEMP
+
+/* Whether the posix_fallocate function exists */
+#mesondefine HAVE_POSIX_FALLOCATE
+
+/* Whether the memfd_create function exists */
+#mesondefine HAVE_MEMFD_CREATE

config.h.meson

@@ -375,6 +375,20 @@ if cc.has_header_symbol('sys/prctl.h', 'prctl')
   cdata.set('HAVE_SYS_PRCTL', 1)
 endif
 
+optional_functions = [
+  'mkostemp',
+  'posix_fallocate',
+  'memfd_create',
+]
+
+foreach function : optional_functions
+  if cc.has_function(function)
+    cdata.set('HAVE_' + function.to_upper(), 1)
+  else
+    message('Optional function ' + function + ' missing')
+  endif
+endforeach
+
 have_xwayland_initfd = false
 have_xwayland_listenfd = false