Fix off-by-one bug in utf16 conversion (PR preprocessor/41698).

libcpp:
2014-11-29  John Schmerge  <jbschmerge@gmail.com>

	PR preprocessor/41698
	* charset.c (one_utf8_to_utf16): Do not produce surrogate pairs
	for 0xffff.

gcc/testsuite:
2014-11-29  Joseph Myers  <joseph@codesourcery.com>

	PR preprocessor/41698
	* gcc/testsuite/g++.dg/cpp/utf16-pr41698-1.C: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@218179 138bc75d-0d04-0410-961f-82ee72b054a4