[flang] Handle subprogram declaration after call

If an external subprogram is called and then declared, we have to
replace the `ProcEntityDetails` with `SubprogramDetails` in the symbol.
While doing so we can also check that the call was consistent with the
declaration for function vs. subprogram.

Original-commit: flang-compiler/f18@e43a2dae790cd0f54ecaec2ffc1235fd2b7754e9
Reviewed-on: https://github.com/flang-compiler/f18/pull/305
Tree-same-pre-rewrite: false