Update from gnulib

Update from gnulib

This incorporates:
2016-08-30 intprops: tune INT_NEGATE_OVERFLOW for GCC 5 and 6
2016-08-29 xalloc-oversized.h: port change to GCC 6.2.0
2016-08-29 intprops.h: port recent changes to GCC 6.2.0
2016-08-29 intprops.h: use __typeof__ with GCC 7
2016-08-29 intprops.h, xalloc-oversized.h: work with gcc 7
2016-08-24 intprops: fix paren typo on old platforms
2016-08-24 intprops: port to OpenVMS
* lib/intprops.h, lib/xalloc-oversized.h: Copy from gnulib.