Signed-off-by: Michael Brown <mcb30@ipxe.org>

Some newer versions of gcc (observed with a patched gcc 4.5.1) seem to
treat our offsetof() implementation as not being a compile-time
constant.  Fix by using __builtin_offsetof() when available.  (As with
the original offsetof() macro, this code is copied from the Linux
kernel's stddef.h.)

Reported-by: Arkadiusz Miskiewicz <arekm@maven.pl>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

gcc defines the magic __WCHAR_TYPE__ macro, in order to convey
information about whether or not the user selected -fshort-wchar.

the definition of it uses offsetof(), and the two concepts are related.