gnulib: update to 776af40e0

This fixes PR27184, a failure to compile gdb due to
cdefs.h being out of sync with glibc on ppc64le targets
which are compiled with -mabi=ieeelongdouble and glibc
2.32.

Likewise, update usage of _GL_ATTRIBUTE_FORMAT_PRINTF to
_GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD.

Likewise, disable newly added rpl_free gnulib api in
gdbserver support libraries.

Likewise, undefine read/write macros before redefining them
on mingw targets.

Likewise, wrap C++ usage of free with GNULIB_NAMESPACE namespace
as needed.

Change-Id: I86517613c0d8ac8f5ea45bbc4ebe2b54a3aef29f

gnulib/import/free.c

@@ -0,0 +1,47 @@
+/* Make free() preserve errno.
+
+   Copyright (C) 2003, 2006, 2009-2021 Free Software Foundation, Inc.
+
+   This program 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 of the License, or
+   (at your option) any later version.
+
+   This program 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 program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* written by Paul Eggert */
+
+#include <config.h>
+
+#include <stdlib.h>
+
+#include <errno.h>
+
+void
+rpl_free (void *p)
+#undef free
+{
+#if defined __GNUC__ && !defined __clang__
+  /* An invalid GCC optimization
+     <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98396>
+     would optimize away the assignments in the code below, when link-time
+     optimization (LTO) is enabled.  Make the code more complicated, so that
+     GCC does not grok how to optimize it.  */
+  int err[2];
+  err[0] = errno;
+  err[1] = errno;
+  errno = 0;
+  free (p);
+  errno = err[errno == 0];
+#else
+  int err = errno;
+  free (p);
+  errno = err;
+#endif
+}