https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91980
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I think the problem is the define for complex is in a system header which causes the error not to happen due to -Wno-system-headers being the default. This is a known issue in newer versions of GCC. There might be another bug for the similar issue.
