c++: fix ICE on FUNCTION_DECLs inside coroutines [PR115906]
When register_local_var_uses iterates a BIND_EXPRs BIND_EXPR_VARS, it
fails to account for the fact that FUNCTION_DECLs might be present, and
later passes it to DECL_HAS_VALUE_EXPR_P. This leads to a tree check
failure in DECL_HAS_VALUE_EXPR_P:
tree check: expected var_decl or parm_decl or result_decl, have
function_decl in register_local_var_uses
We only care about PARM_DECL and VAR_DECL, so select only those.
PR c++/115906 - [coroutines] missing diagnostic and ICE when co_await used as default argument in function declaration
gcc/cp/ChangeLog:
PR c++/115906
* coroutines.cc (register_local_var_uses): Only process
PARM_DECL and VAR_DECLs.
gcc/testsuite/ChangeLog:
PR c++/115906
* g++.dg/coroutines/coro-function-decl.C: New test.