Sync libiberty sources with GCC mainline.

Sync libiberty sources with GCC mainline.

Brings in:
  2017-01-18  Markus Trippelsdorf  <markus@trippelsdorf.de>

	PR PR c++/70182
	* cp-demangle.c (d_unqualified_name): Handle "on" for
	operator names.
	* testsuite/demangle-expected: Add tests.

 2017-01-18  Markus Trippelsdorf  <markus@trippelsdorf.de>

	PR c++/77489
	* cp-demangle.c (d_discriminator): Handle discriminator >= 10.
	* testsuite/demangle-expected: Add tests for discriminator.

 2016-12-13  Jakub Jelinek  <jakub@redhat.com>

	PR c++/78761
	* cp-demangle.c (cplus_demangle_type): Demangle Dc as decltype(auto).
	* testsuite/demangle-expected: Add test for decltype(auto).