Another major advance in scansys.py sophistication.

 * We now distinguish headers that don't exist at all from headers that
   exist but provoke errors when preprocessed (e.g. via #error).  This
   feature depends on parsing compiler output, so the smoke tests make
   sure it understands your compiler.

 * Headers which don't exist are mentioned in inventory output (with a
   leading minus sign) so that we can tell "doesn't exist" from "no data".

 * <endian.h> added to b-ucom, <arpa/nameser_compat.h> noted to potentially
   depend on it (suspected cause of current !arpa/nameser_compat.h on QNX).
Regenerate GNU libc and Android inventories with updated scansys.
FINALLY, --recheck works on Windows without having to be in the right
console window.

Also regenerate Windows inventories with latest scansys.