objc++: type/expr tsubst conflation [PR111920]

objc++: type/expr tsubst conflation [PR111920]

After r14-4796-g3e3d73ed5e85e7, tsubst_copy_and_build (now named
tsubst_expr) no longer dispatches to tsubst for type trees, and
callers have to do it themselves if appropriate.  This patch makes
some overlooked adjustments to Objective-C++-specific code paths.

	PR objc++/111920

gcc/cp/ChangeLog:

	* pt.cc (tsubst_expr) <case AT_ENCODE_EXPR>: Use tsubst instead
	of tsubst_expr.

gcc/objcp/ChangeLog:

	* objcp-lang.cc (objcp_tsubst_expr) <case CLASS_REFERENCE_EXPR>:
	Use tsubst instead of tsubst_expr for type operands.