c++: non-dependent call to consteval operator [PR105912]
Here we're crashing when substituting a non-dependent call to a
consteval operator, whose CALL_EXPR_OPERATOR_SYNTAX flag we try to
propagate to the result, but the result isn't a CALL_EXPR since the
selected function is consteval. This patch fixes this by checking the
result of extract_call_expr accordingly. (Note that we can't check
DECL_IMMEDIATE_FUNCTION_P here because we don't know which function was
selected by overload resolution from here.)
PR c++/105912
gcc/cp/ChangeLog:
* pt.cc (tsubst_copy_and_build) <case CALL_EXPR>: Guard against
NULL_TREE extract_call_expr result.