Update from Gnulib

Update from Gnulib

This incorporates:
2020-08-12 stdint: port intptr_t to more-recent MinGW
2020-08-11 Use __restrict also on clang
2020-08-11 Use flexible array syntax also on clang
2020-08-11 fcntl: On native Windows, use _setmode, not setmode
* lib/binary-io.h, lib/cdefs.h, lib/fcntl.c, lib/regex.h:
* lib/stdint.in.h: Copy from Gnulib.