tests/gl_basic_test: silence implicit-fallthrough warn
tests/gl_basic_test: silence implicit-fallthrough warn

The skip() function from cmocka is missing the noreturn notation. Thus
the compiler assumes that it can return and results in
implicit-fallthrough warnings.

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>

waffle-gl/waffle,waffle-gl/waffle,waffle-gl/waffle,waffle-gl/waffle