[Clang][DebugInfo] Clang generates an extra spurious unnamed 'dbg.declare' (#69681)

Do not emit call to llvm.dbg.declare when the variable declaration
is a DecompositionDecl as its instance class is always unnamed.

The emitted debug declare looks like:

call void @llvm.dbg.declare(metadata ..., metadata !xx, metadata ...)
!xx = !DILocalVariable(scope: !..., file: !..., line: ..., type: !...)