Add internal facility for dynamic array handling

This is intended as a type-safe alternative to obstacks and
hand-written realloc constructs.  The implementation avoids
writing function pointers to the heap.

malloc/dynarray_at_failure.c

@@ -0,0 +1,31 @@
+/* Report an dynamic array index out of bounds condition.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <dynarray.h>
+#include <stdio.h>
+
+void
+__libc_dynarray_at_failure (size_t size, size_t index)
+{
+  char buf[200];
+  __snprintf (buf, sizeof (buf), "Fatal glibc error: "
+              "array index %zu not less than array length %zu\n",
+              index, size);
+ __libc_fatal (buf);
+}
+libc_hidden_def (__libc_dynarray_at_failure)