Flags were not correctly set for symbols appearing in the OpenACC declare
directive in module declaration part.
Also some missing flags for OpenACC are added. This makes the Flags enum
64 and then the implementation switch to std::bitset as defined in
flang/include/flang/Common/enum-set.h. Therefore, constexpr cannot be
used for set of flags in flang/lib/Semantics/resolve-directives.cpp.
Should present be a data sharing attribute instead of data mapping attribute?