GTK+ gcc: undefined reference to all gtk functions when linking

The order is wrong: this is an incredibly common mistake I continue to meet. Previous versions of gcc were less picky on the argument order and this spread the wrong idea pkgconfig --cflags --libs works in every position.

Check out this email for info on proper flags ordering. In short:

gcc $(pkg-config --cflags ...) myapp.c $(pkg-config --libs ...)