coroutines: Fix for uses of structured binding [PR94701]

coroutines: Fix for uses of structured binding [PR94701]

Structured binding makes use of the DECL_VALUE_EXPR fields
in local variables.  We need to recognise these and only amend
the expression values, retaining the 'alias' value intact.

gcc/cp/ChangeLog:

2020-04-27  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94701
	* coroutines.cc (struct local_var_info): Add fields for static
	variables and those with DECL_VALUE_EXPR redirection.
	(transform_local_var_uses):  Skip past typedefs and static vars
	and then account for redirected variables.
	(register_local_var_uses): Likewise.

gcc/testsuite/ChangeLog:

2020-04-27  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94701
	* g++.dg/coroutines/torture/local-var-06-structured-binding.C: New test.