add the cleanup checker

This patch adds the cleanup checker.  This is a Python plugin for GCC
that checks some rules for cleanup handling.  In particular it tries
to notice when cleanups are left dangling at the end of a function.

It does this by applying a few simple rules.

First, it understands that a function whose return type is "struct
cleanup *" is a "cleanup constructor".  Such functions are expected to
return the first cleanup that they make.

Then, it has the notion of a "master cleanup".  The checker keeps a
stack of all cleanups made in a basic block.  The first element is
pushed on the stack is the master cleanup -- the one that must later
be passed to either do_cleanups or discard_cleanups.

It is not perfect -- some constructs confuse it.  So, part of this
series rewrites some code in gdb so that it is analyzable.  I'll note
these spots and you can decide whether or not this is a good idea.

This patch also changes gcc-with-excheck to give it options.  Now you
must use either -Xc (for the cleanup checker) or -Xx (for the
exception checker).

	* contrib/cleanup_check.py: New file.
	* contrib/gcc-with-excheck: Add option parsing.
some cleanup checker fixes

Fix some bugs pointed out by the cleanup checker.  This one just fixes
some simple CLI reports, where CLI commands know that their caller
will do cleanups.  This an older style with few instances, so it is
simpler to fix them up than to teach the checker about it.

	* cli/cli-cmds.c (cd_command, alias_command): Call do_cleanups.
	* cli/cli-dump.c (restore_binary_file): Call do_cleanups.
	* interps.c (interpreter_exec_cmd): Call do_cleanups.
	* source.c (show_substitute_path_command): Call do_cleanups.
	(unset_substitute_path_command, set_substitute_path_command):
	Likewise.
	* symfile.c (load_command): Call do_cleanups.
fix print_command_1

This is a stylistic patch to make it so the checker can analyze
print_command_1.  This amounts to installing an outer cleanup and
unconditionally invoking it.

	* printcmd.c (print_command_1): Unconditionally call do_cleanups.
fix cleanups in som_symtab_read

This fixes som_symtab_read not to leak cleanups.

	* somread.c (som_symtab_read): Call do_cleanups.
remove erroneous return from setup_user_args

This fixes setup_user_args to drop a useless and confusing "return".

	* cli/cli-script.c (setup_user_args): Don't return after error.
fix linespec bug noticed by the checker

This fixes a linespec bug noticed by the cleanup checker.

find_linespec_symbols did this:

  cleanup = demangle_for_lookup (name, state->language->la_language,
				 &lookup_name);
[...]
      cleanup = make_cleanup (xfree, canon);

But this is wrong, as it makes a subsequent call to do_cleanups not
clean up all the local state.

	* linespec.c (find_linespec_symbols): Don't reassign to 'cleanup'.