[committed] coroutines: ensure placeholder var is properly declared.

[Iain Sandoe]

Hi,

An omission spotted while working on open PRs.
tested on x86_64-linux/darwin, applied to master as obvious.
thanks
Iain
    
In cases that we need to extended the lifetime of a temporary captured
by reference, we make a replacement var for the temporary.  This will
be then used to define a coroutine frame entry (so that the var created
is elided by a later phase).  However, we should ensure that the var
is correctly declared anyway.

gcc/cp/ChangeLog:
    
2020-04-07  Iain Sandoe  <i...@sandoe.co.uk>
    
        * coroutines.cc (maybe_promote_captured_temps): Ensure that
        reference capture placeholder vars are properly declared.

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 38a23a91f8b..983fa650b55 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -2832,7 +2832,9 @@ maybe_promote_captured_temps (tree *stmt, void *d)
            sloc = DECL_SOURCE_LOCATION (orig_temp);
          DECL_SOURCE_LOCATION (newvar) = sloc;
          DECL_CHAIN (newvar) = varlist;
-         varlist = newvar;
+         varlist = newvar; /* Chain it onto the list for the bind expr.  */
+         /* Declare and initialze it in the new bind scope.  */
+         add_decl_expr (newvar);
          tree stmt
            = build2_loc (sloc, INIT_EXPR, var_type, newvar, to_replace);
          stmt = coro_build_cvt_void_expr_stmt (stmt, sloc);