XOUTPUT_METHOD: default to true

XOpenOM() has been a core part of xlib for some time.

For now, hard-code this to always be true -- this can be
clearned up at a later date.

meson.build

@@ -74,6 +74,7 @@ conf.set('SIGNAL_RETURN', 'return')
 conf.set('ICONV_ARG_CONST', '')
 conf.set('fd_set_size_t', 'int')
 conf.set('EXECUTABLE_EXTENSION', 'NULL')
+conf.set10('HAVE_XOUTPUT_METHOD', true)
 
 # Enable FTMs
 if host_machine.system() == 'linux'