[clang] Add '-ast-dump-filter=' support

[oToToT]

Summary

Before this patch, we only support syntax like
clang -cc1 -ast-dump -ast-dump-filter main a.c
or
clang -Xclang -ast-dump -Xclang -ast-dump-filter -Xclang main a.c
when using ast-dump-filter.

It is helpful to also support -ast-dump-filter= syntax, so we can do something like
clang -cc1 -ast-dump -ast-dump-filter=main a.c
or
clang -Xclang -ast-dump -Xclang -ast-dump-filter=main a.c

It is more cleaner when passing arguments through -Xclang in this case.

Also, clang-check do support this syntax, and I think people might be confused when they found they can't use -ast-dump-filter with clang.

[oToToT]

ping

[dblaikie]

Sure, sounds OK!

clang/include/clang/Driver/Options.td

def add_plugin : Separate<["-"], "add-plugin">, MetaVarName<"<name>">,
   HelpText<"Use the named plugin action in addition to the default action">,
   MarshallingInfoStringVector<FrontendOpts<"AddPluginActions">>;
 def ast_dump_filter : Separate<["-"], "ast-dump-filter">,
   MetaVarName<"<dump_filter>">,
   HelpText<"Use with -ast-dump or -ast-print to dump/print only AST declaration"
            " nodes having a certain substring in a qualified name. Use"
            " -ast-list to list all filterable declaration node names.">,
   MarshallingInfoString<FrontendOpts<"ASTDumpFilter">>;
+def ast_dump_filter_EQ : Joined<["-"], "ast-dump-filter=">,
+  Alias<ast_dump_filter>;
 def fno_modules_global_index : Flag<["-"], "fno-modules-global-index">,
   HelpText<"Do not automatically generate or update the global module index">,
   MarshallingInfoNegativeFlag<FrontendOpts<"UseGlobalModuleIndex">>;
 def fno_modules_error_recovery : Flag<["-"], "fno-modules-error-recovery">,
   HelpText<"Do not automatically import modules for error recovery">,
   MarshallingInfoNegativeFlag<LangOpts<"ModulesErrorRecovery">>;
 def fmodule_map_file_home_is_cwd : Flag<["-"], "fmodule-map-file-home-is-cwd">,
   HelpText<"Use the current working directory as the home directory of "