[flang] Fix generic/specific procedure confusion

[flang] Fix generic/specific procedure confusion

A recent change that extended semantic analysis for actual arguments
that associate with procedure dummy arguments exposed some bugs in
regression test suites due to points of confusion in symbol table
handling in situations where a generic interface contains a specific
procedure of the same name.  When passing that name as an actual
argument, for example, it's necessary to take this possibility into
account because the symbol for the generic interface shadows the
symbol of the same name for the specific procedure, which is
what needs to be checked.  So add a small utility that bypasses
the symbol for a generic interface in this case, and use it
where needed.

Differential Revision: https://reviews.llvm.org/D104929