Merge from gnulib.

Merge from gnulib.

* lib/filemode.h, lib/signal.in.h, lib/stat.c, lib/stdint.in.h:
* lib/stdlib.in.h, lib/unistd.in.h, m4/extensions.m4, m4/getloadavg.m4:
* m4/getopt.m4, m4/gnulib-common.m4, m4/largefile.m4, m4/mktime.m4:
* m4/multiarch.m4, m4/nocrash.m4, m4/stdio_h.m4, m4/time_r.m4:
Copy new versions from gnulib, incorporating the following changes:
2012-06-22 time_r: fix typo that always overrode localtime_r decl
2012-06-22 Write "Mac OS X" instead of "MacOS X".
2012-06-21 mktime: fix integer overflow in 'configure'-time test
2012-06-21 nonblocking: Avoid compilation error on mingw64.
2012-06-19 stat, fstat: Avoid warnings on mingw64.
2012-06-19 getopt-gnu: Fix exit code overflow in autoconf test.