c++: constantness of call to function pointer [PR111703]
potential_constant_expression for CALL_EXPR tests FUNCTION_POINTER_TYPE_P
on the callee rather than on the type of the callee, which means we
always pass want_rval=any when recursing and so may fail to identify a
non-constant function pointer callee as such. Fixing this turns out to
further work around PR111703.
PR c++/111703
PR c++/107939
gcc/cp/ChangeLog:
* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
Fix FUNCTION_POINTER_TYPE_P test.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-fn8.C: Extend test.
* g++.dg/diagnostic/constexpr4.C: New test.