[PR c++/84968] reject stmt-exprs in noexcept constexprs

[PR c++/84968] reject stmt-exprs in noexcept constexprs

We reject extended statement-expressions in template parameters, so we
might as well reject them in constant expressions used in noexcept
specifications.

for  gcc/cp/ChangeLog

	PR c++/84968
	* tree.c (strip_typedefs_expr): Reject STATEMENT_LISTs.

for  gcc/testsuite/ChangeLog

	PR c++/84968
	* g++.dg/eh/pr84968.C: New.

From-SVN: r258913