meson: build gir even when cross-compiling if introspection was enabl…

…ed explicitly

This can be made to work in certain circumstances when
cross-compiling, so default to not building g-i stuff
when cross-compiling, but allow it if introspection was
enabled explicitly via -Dintrospection=enabled.

See gstreamer/gstreamer#454 and gstreamer/gstreamer#381.

meson.build

@@ -372,7 +372,7 @@ endif
 
 gir = find_program('g-ir-scanner', required : get_option('introspection'))
 gnome = import('gnome')
-build_gir = gir.found() and not meson.is_cross_build()
+build_gir = gir.found() and (not meson.is_cross_build() or get_option('introspection').enabled())
 gir_init_section = [ '--add-init-section=extern void gst_init(gint*,gchar**);' + \
     'g_setenv("GST_REGISTRY_DISABLE", "yes", TRUE);' + \
     'g_setenv("GST_REGISTRY_1.0", "@0@", TRUE);'.format(meson.current_build_dir() + '/gir_empty_registry.reg') + \