Older versions of Clang (before 3.5) and GCC (before 4.1) do not
support the "__attribute__((flatten))" yet. We don't care about
such old versions of GCC anymore, but since Clang 3.4 is still
used in EPEL for RHEL7 / CentOS 7, we should not use this attribute
directly but with a wrapper macro instead.
Reviewed-by: Alex Bennée <email@example.com>
Reviewed-by: Richard Henderson <firstname.lastname@example.org>
Signed-off-by: Thomas Huth <email@example.com>