Fix bug #11279 with sending command blocks to GDB.

Fix bug #11279 with sending command blocks to GDB.

 lisp/progmodes/gdb-mi.el (gdb-control-level): New variable.
 (gdb): Make it buffer-local and init to zero.
 (gdb-control-commands-regexp): New variable.
 (gdb-send): Don't wrap in "-interpreter-exec console" if
 gdb-control-level is positive.  Increment gdb-control-level
 whenever the command matches gdb-control-commands-regexp, and
 decrement it each time the command is "end".  (Bug#11279)