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/dup.c

@@ -1,6 +1,6 @@
 /* Duplicate an open file descriptor.
 
-   Copyright (C) 2011-2020 Free Software Foundation, Inc.
+   Copyright (C) 2011-2021 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
@@ -28,7 +28,8 @@
 
 #undef dup
 
-#if HAVE_MSVC_INVALID_PARAMETER_HANDLER
+#if defined _WIN32 && !defined __CYGWIN__
+# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
 static int
 dup_nothrow (int fd)
 {
@@ -36,7 +37,7 @@ dup_nothrow (int fd)
 
   TRY_MSVC_INVAL
     {
-      result = dup (fd);
+      result = _dup (fd);
     }
   CATCH_MSVC_INVAL
     {
@@ -47,6 +48,9 @@ dup_nothrow (int fd)
 
   return result;
 }
+# else
+#  define dup_nothrow _dup
+# endif
 #elif defined __KLIBC__
 # include <fcntl.h>
 # include <sys/stat.h>