pango: add printf attribute

This allows the compiler to catch mismatches between the format
string and the arguments passed in.

Need to add -Wno-format-zero-length because we pass an empty string
on purpose in swaybar/render.c.

meson.build

@@ -18,6 +18,7 @@ add_project_arguments(
 		'-Wno-unused-parameter',
 		'-Wno-unused-result',
 		'-Wno-missing-braces',
+		'-Wno-format-zero-length',
 		'-Wundef',
 		'-Wvla',
 	],