max_align_t does not depend on any pre-C99 or !C++ language feature.
This structure is in use in 3rd party essential C++ code as an extension
for older language revisions and in gnu99 code in the NetBSD distribution
(RTLD's build rules define -std=gnu11 just for exposing this struct).
Exposing max_align_t from the central NetBSD header avoid duplicate
definition in 3rd party code that could differ and produce ABI mismatched
binaries between -std= revisions.
This problem does not exist on OSs like Linux as they get this namespace
visibility defined inside LLVM or GNU toolchain headers. NetBSD ships with
its own stddef.h, rather than relying on a toolchain and its internal
extensions.
From the redhat web page:
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/gcc/offsetof.html
__offsetof__ (expression)
is equivalent to the parenthesized expression, except that the
expression is considered an integral constant expression even if
it contains certain operators that are not normally permitted in
an integral constant expression. Users should never use __offsetof__
directly; the only valid use of __offsetof__ is to implement the
offsetof macro in <stddef.h>.
g++-3 does not have a built-in offsetof(), but we cannot use the c version,
otherwise we break with -Wold-style-cast.
Inspired by the DF version, but a bit different.
as __null with egcs 1.0 (GCC 2.90) and above. As several headers are affected
by this change, move the definition into a new header file, <null.h>, to ease
maintenance.
joerg