https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124238
--- Comment #19 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Note, including any C++ headers like that #include <iostream> is wrong in the
FEs and elsewhere in the compiler, because system.h poisons tons of symbols
that the C++ headers can use. That is why we instead have #define
INCLUDE_{DEQUE,LIST,MAP,SET,STRING,VECTOR,ARRAY,FUNCTIONAL,SSTREAM}.
There is no point to add iostream to that list because iostream really
shouldn't be used in the compiler, for diagnostics we have our own diagnostic
library.
