the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.
installation docs have also been updated to reflect this change.
note that POSIX does not specify these functions as _Noreturn, because
POSIX is aligned with C99, not the new C11 standard. when POSIX is
eventually updated to C11, it will almost surely give these functions
the _Noreturn attribute. for now, the actual _Noreturn keyword is not
used anyway when compiling with a c99 compiler, which is what POSIX
requires; the GCC __attribute__ is used instead if it's available,
however.
in a few places, I've added infinite for loops at the end of _Noreturn
functions to silence compiler warnings. presumably
__buildin_unreachable could achieve the same thing, but it would only
work on newer GCCs and would not be portable. the loops should have
near-zero code size cost anyway.
like the previous _Noreturn commit, this one is based on patches
contributed by philomath.
Rich Felker