This caused GCC 6.3.0 -Winline to complain:
../../../ext/libglnx/glnx-errors.h:169:1: warning: function
‘glnx_throw_errno_prefix’ can never be inlined because it uses
variable argument lists [-Winline]
glnx_throw_errno_prefix (GError **error, const char *fmt, ...)
^~~~~~~~~~~~~~~~~~~~~~~
../../../ext/libglnx/glnx-errors.h:169:1: warning: inlining failed
in call to ‘glnx_throw_errno_prefix’: function not inlinable
[-Winline]
We have a *lot* of code of the form:
```
if (unlinkat (fd, pathname) < 0)
{
glnx_set_error_from_errno (error);
goto out;
}
```
After conversion to `return FALSE style` which is in progress, it's way shorter,
and clearer like this:
```
if (unlinkat (fd, pathname) < 0)
return glnx_throw_errno (error);
```
