gdb: Introduce global_symbol_searcher

gdb: Introduce global_symbol_searcher

Introduce a new class to wrap up the parameters needed for the
function search_symbols, which has now become a member function of
this new class.

The motivation is that search_symbols already takes a lot of
parameters, and a future commit is going to add even more.  This
commit hopefully makes collecting the state required for a search
easier.

As part of this conversion the list of filenames in which to search
has been converted to a std::vector.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* python/python.c (gdbpy_rbreak): Convert to using
	global_symbol_searcher.
	* symtab.c (file_matches): Convert return type to bool, change
	file list to std::vector, update header comment.
	(search_symbols): Rename to...
	(global_symbol_searcher::search): ...this and update now its
	a member function of global_symbol_searcher.  Take account of the
	changes to file_matches.
	(symtab_symbol_info): Convert to using global_symbol_searcher.
	(rbreak_command): Likewise.
	(search_module_symbols): Likewise.
	* symtab.h (enum symbol_search): Update comment.
	(search_symbols): Remove declaration.
	(class global_symbol_searcher): New class.

Change-Id: I488ab292a892d9e9e84775c632c5f198b6ad3710