[OpenMP][Clang] Enable inscan modifier for generic datatypes (#82220)

This patch fixes the #67002 ([OpenMP][Clang] Scan Directive not
supported for Generic types). It disables the Sema checks/analysis that
are run on the helper arrays which go into the implementation of the
`omp scan` directive until the template instantiation happens.
Grateful to @alexey-bataev for suggesting these changes.