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/rlbasic.c

@@ -0,0 +1,29 @@
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+
+#if defined (READLINE_LIBRARY)
+#  include "readline.h"
+#  include "history.h"
+#else
+#  include <readline/readline.h>
+#  include <readline/history.h>
+#endif
+
+int
+main (int c, char **v)
+{
+	char *input;
+
+	for (;;) {
+		input = readline ((char *)NULL);
+		if (input == 0)
+			break;
+		printf ("%s\n", input);
+		if (strcmp (input, "exit") == 0)
+			break;
+		free (input);
+	}
+	exit (0);
+}