[patch] libstdc++/66855 ignore endianness in codecvt_utf8_utf16

[Jonathan Wakely <jwakely at redhat dot com>]

This facet is not meant to pay attention to mode|little_endian, so
explicitly override the value to output with the target's native
endianness.

Tested powerpc64-linux and powerp64le-linux, committed to trunk.

I'll commit it to the gcc-5-branch after the 5.2 release.

commit e35e03773955a618cba43fcef4b1559ba9a27d8c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jul 13 19:38:58 2015 +0100

    	PR libstdc++/66855
    	* src/c++11/codecvt.cc (__codecvt_utf8_utf16_base::do_in): Override
    	endianness bit in mode.
    	* testsuite/22_locale/codecvt/codecvt_utf8_utf16/66855.cc: New.

diff --git a/libstdc++-v3/src/c++11/codecvt.cc b/libstdc++-v3/src/c++11/codecvt.cc
index 6b82aa8..a454064 100644
--- a/libstdc++-v3/src/c++11/codecvt.cc
+++ b/libstdc++-v3/src/c++11/codecvt.cc
@@ -1264,7 +1264,11 @@ do_in(state_type&, const extern_type* __from, const extern_type* __from_end,
 {
   range<const char> from{ __from, __from_end };
   range<char16_t> to{ __to, __to_end };
-  auto res = utf16_in(from, to, _M_maxcode, _M_mode);
+  codecvt_mode mode = codecvt_mode(_M_mode | (consume_header|generate_header));
+#if __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__
+  mode = codecvt_mode(mode | little_endian);
+#endif
+  auto res = utf16_in(from, to, _M_maxcode, mode);
   __from_next = from.next;
   __to_next = to.next;
   return res;
diff --git a/libstdc++-v3/testsuite/22_locale/codecvt/codecvt_utf8_utf16/66855.cc b/libstdc++-v3/testsuite/22_locale/codecvt/codecvt_utf8_utf16/66855.cc
new file mode 100644
index 0000000..3f99cb4
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/codecvt/codecvt_utf8_utf16/66855.cc
@@ -0,0 +1,52 @@
+// Copyright (C) 2015 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++11" }
+
+#include <codecvt>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::codecvt_utf8_utf16<char16_t> cvt;
+  char16_t utf16[] = u"\ub098\ub294\ud0dc\uc624";
+  const char16_t* nf16;
+  char utf8[16];
+  char* nt8;
+  std::mbstate_t st{};
+  auto res = cvt.out(st, utf16, utf16+4, nf16, utf8, utf8+16, nt8);
+  VERIFY( res == std::codecvt_base::ok );
+
+  st = {};
+  char16_t buf[4] = {};
+  const char* nf8 = nt8;
+  char16_t* nt16;
+  res = cvt.in(st, utf8, nf8, nf8, buf, buf+4, nt16);
+  VERIFY( res == std::codecvt_base::ok );
+  VERIFY( nt16 == buf+4 );
+  VERIFY( buf[0] == utf16[0] );
+  VERIFY( buf[1] == utf16[1] );
+  VERIFY( buf[2] == utf16[2] );
+  VERIFY( buf[3] == utf16[3] );
+}
+
+int
+main()
+{
+  test01();
+}