https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57025
--- Comment #8 from ro at CeBiTec dot Uni-Bielefeld.DE <ro at CeBiTec dot Uni-Bielefeld.DE> --- > --- Comment #7 from Alan Coopersmith <alan.coopersmith at oracle dot com> --- > This seems to go back to: > https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=a6905708d86d6c2d8560168ac5accb816a2038c8 > and was probably to deal with the bit of the Solaris system headers in > various releases that throws an error if you try to define _XOPEN_SOURCE > to 600 or 700 and didn't have a __STDC_VERSION__ matching C99 defined. Right: the corresponding patch submission with background info is at https://gcc.gnu.org/ml/gcc-patches/2010-05/msg01308.html. As it happens, a colleague just yesterday ran into the `no C99 without XPG6' issue on some 2016 SRU of Solaris 11.3. Given that those checks were remove only later, I fear the current code in g++ has to stay for those not on the latest bits (like non-support users).
