[Bug libstdc++/59087] Issues including complex.h in C++11/1y mode because of C's complex.h

[vlovich at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59087

--- Comment #12 from Vitali <vlovich at gmail dot com> ---
Actually, http://en.cppreference.com/w/cpp/header seems to indicate that when
compiling as C++, complex.h should be equal to including ccomplex in a global
namespace.  It seems like the inclusion of C99 complex.h is a GNU extension &
should only be done if GNU extensions are enabled.