[mlir][debug] Support DICommonBlock. (#111706)
A COMMON block is a named area of memory that holds a collection of
variables. Fortran subprograms may map the COMMON block memory area to a
list of variables. A common block is represented in LLVM debug by
DICommonBlock.
This PR adds support for this in MLIR. The changes are mostly mechanical
apart from small change to access the DICompileUnit when the scope of
the variable is DICommonBlock.
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Co-authored-by: Tobias Gysi <tobias.gysi@nextsilicon.com>
