Stop emit incomplete type error for a variable in a map clause

where should not.

Currently we are using QTy->isIncompleteType(&ND) to check incomplete
type.  But before doing that, need to instantiate for a class template
specialization or a class member of a class template specialization,
or an array with known size of such..., so that we know it is really
incomplete type.

To fix this using RequireCompleteType instead.

The new test is added into "test/OpenMP/target_update_messages.cpp"

The different of using RequireCompleteType is when emit incomplete type,
an additional note is also emitted to point to where incomplete type
is declared.  Because this change, many tests are needed to be fixed
by adding additional note.

This is to fix https://bugs.llvm.org/show_bug.cgi?id=50508

Differential Revision: https://reviews.llvm.org/D107200