c++: double non-dep folding from finish_compound_literal [PR104565]
In finish_compound_literal, we perform non-dependent expr folding before
the call to check_narrowing ever since r9-5973. But ever since r10-7096,
check_narrowing also performs non-dependent expr folding of its own.
This double folding means tsubst will see non-templated trees during the
second folding, which causes a spurious error in the below testcase.
This patch removes the former folding operation; it seems obviated by
the latter one.