In GSK the following pattern is used four times:
```
switch (self->filter)
{
default:
g_assert_not_reached ();
G_GNUC_FALLTHROUGH;
case GSK_GPU_BLIT_LINEAR:
filter = GL_LINEAR;
break;
case GSK_GPU_BLIT_NEAREST:
filter = GL_NEAREST;
break;
}
```
The G_GNUC_FALLTHROUGH macro is not required. When G_DISABLE_ASSERT
is defined the body of the `default` case is empty, thus there is
no need. When G_DISABLE_ASSERT is not defined the body of the `default`
case contains g_assert_not_reached() thus it won't fallthrough.
This resolves the following:
```
[221/1379] Compiling C object gsk/libgsk.a.p/gpu_gskgpublitop.c.o
[...]
error: fallthrough annotation in unreachable code [-Werror,-Wimplicit-fallthrough]
1 error generated.
```
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