Merge from gnulib

Merge from gnulib

This incorporates:
2016-11-15 sys_time: add gnulib::timeval for C++
2016-11-14 snippet/c++defs: fix real-floating arg functions in C++ mode
2016-11-13 strftime: don't use __THROW
2016-11-12 strftime: tune %q
2016-11-12 Merge strftime.c changes from glibc
2016-11-09 manywarnings: fix -Wno-missing-field-initializers detection
2016-11-05 strftime,strptime: support %q to represent the quarter

The glibc changes in turn incorporate the following strftime.c changes:
2015-10-20 Convert misc function definitions to prototype style
2015-09-26 [BZ #18985] out of range data to strftime() causes segfault
2010-01-09 Add support for XPG7 testing
2009-10-30 Implement Burmese language locale for Myanmar
2008-06-13 [BZ #6612] pass reference to tzset_called around
2007-10-16 [BZ #5184] Add tzset_called argument

* build-aux/snippet/c++defs.h, lib/strftime.c, lib/sys_time.in.h:
* m4/manywarnings.m4: Copy from gnulib.