[libcp1] handle anon aggregates linkage-named by typedefs

[libcp1] handle anon aggregates linkage-named by typedefs

Arrange for the first typedef to an anonymous type in the same context
to be used as the linkage name for the type.

for  gcc/cp/ChangeLog

	* decl.c (name_unnamed_type): Split out of...
	(grokdeclarator): ... this.
	* decl.h (name_unnamed_type): Declare.

for  libcc1/ChangeLog

	* libcp1plugin.cc (plugin_build_decl): Call name_unnamed_type.

From-SVN: r246938