build: Lift gir and build_gir to toplevel

build_gir is used in multiple subdirectories,
so it is a bit nasty that it is defined in
one too.

gtk/meson.build

@@ -1180,9 +1180,6 @@ libgtk = shared_library('gtk-4',
 gtk_dep_sources = [gtkversion, gtktypebuiltins_h]
 
 # Introspection
-gir = find_program('g-ir-scanner', required : get_option('introspection'))
-build_gir = gir.found() and (not meson.is_cross_build() or get_option('introspection').enabled())
-
 if build_gir
   gir_args = [
     '-DGTK_COMPILATION',

meson.build

@@ -728,6 +728,11 @@ int main () {
   endif
 endif
 
+# Introspection
+gir = find_program('g-ir-scanner', required : get_option('introspection'))
+build_gir = gir.found() and (not meson.is_cross_build() or get_option('introspection').enabled())
+
+
 project_build_root = meson.current_build_dir()
 
 subdir('gtk/css')