tests: Make leak check work again by setting default visibility for malloc/free
tests: Make leak check work again by setting default visibility for malloc/free

We compile the test cases with -fvisibility=hidden which makes
our malloc/free wrappers fail to override system malloc/free.

eyolfson/wayland,abooij/wayland,mchalupa/wayland,abooij/wayland,sir-murray/wayland,sir-murray/wayland,mchalupa/wayland,mchalupa/wayland,sir-murray/wayland,eyolfson/wayland,bitfactor/wayland,eyolfson/wayland,bitfactor/wayland,abooij/wayland,tulcod/wayland,tulcod/wayland,bitfactor/wayland,tulcod/wayland