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/rl.c

@@ -28,6 +28,7 @@
 #  include <config.h>
 #endif
 
+#include <unistd.h>
 #include <stdio.h>
 #include <sys/types.h>