[flang] [llvm] [mlir] [Flang][OpenMP][MLIR] Fix common block mapping for regular and declare target link (PR #91829)

[via llvm-commits]

agozillon wrote:

> Was there an initial patch that added support for common block mapping? If so, could you give me a link?

There was not, I believe we just assumed it was working after some prior testing but the tests were not quite correct unfortunately, so this PR allows it to appropriately function when declare target link'd (but no declare target to) and regular mapped explicit/implicit at least from testing so far.

https://github.com/llvm/llvm-project/pull/91829