Import readline 7.0 (patch 5)

This imports readline 7.0 (up to patch 5) while preserving all
gdb-local changes.

This was done by checking out the readline git repository, making a
branch based on the gdb baseline revision, applying the gdb changes to
that branch, and then merging from readline 7.

readline/ChangeLog.gdb
2019-08-12  Tom Tromey  <tom@tromey.com>

	* Imported readline 7.0 patch 5.

readline/examples/excallback.c

@@ -40,13 +40,14 @@ Copyright (C) 1999 Jeff Solomon
 #include <config.h>
 #endif
 
-#include <stdio.h>
 #include <sys/types.h>
 
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#include <stdlib.h>
 
+#include <stdio.h>
 #include <termios.h>	/* xxx - should make this more general */
 
 #ifdef READLINE_LIBRARY
@@ -55,6 +56,10 @@ Copyright (C) 1999 Jeff Solomon
 #  include <readline/readline.h>
 #endif
 
+#ifndef STDIN_FILENO
+#  define STDIN_FILENO 0
+#endif
+
 /* This little examples demonstrates the alternate interface to using readline.
  * In the alternate interface, the user maintains control over program flow and
  * only calls readline when STDIN is readable. Using the alternate interface,