[flang] Extension: allow DATA to precede declaration under IMPLICIT NONE(TYPE)

It is not standard conforming under IMPLICIT NONE(TYPE) for a name to
appear in a DATA statement prior to its explicit type declaration,
but it is benign, supported in other compilers, and attested in real
applications.  Support it with an optional portability warning.

Fixes GitHub LLVM bug https://github.com/llvm/llvm-project/issues/63783.