Use exceptions and cleanups in gdbserver

Use exceptions and cleanups in gdbserver

This commit replaces the hacky "exception" system in gdbserver with
the exceptions and cleanups subsystem from GDB.

Only the catch/cleanup code in what was "main" has been updated to
use the new system.  Other parts of gdbserver can now be converted
to use TRY_CATCH and cleanups on an as-needed basis.

A side-effect of this commit is that some error messages will change
slightly, and in cases with multiple errors the error messages will
be printed in a different order.

gdb/gdbserver/ChangeLog:

	* server.h (setjmp.h): Do not include.
	(toplevel): Do not declare.
	(common-exceptions.h): Include.
	(cleanups.h): Likewise.
	* server.c (toplevel): Do not define.
	(exit_code): New static global.
	(detach_or_kill_for_exit_cleanup): New function.
	(main): New function.  Original main renamed to...
	(captured_main): New function.
	* utils.c (verror) [!IN_PROCESS_AGENT]: Use throw_verror.