[clang] [CIR] Add emitDeclInvariant for global with constant storage (PR #171915)

[via cfe-commits]

adams381 wrote:

All reviewer feedback has been addressed:

✅ Parameter naming - Changed to camelCase
✅ Address space handling - Removed dynamic suffix construction
✅ Comment explaining move - Added explanation for constant storage calculation move
✅ Logic consistency - Aligned emitGlobalVarDefinition with classic codegen
✅ Remove CWithDtor case - Removed duplicate test case
✅ Reorganize test checks - Interleaved checks by test case
✅ Add checks for before/after LoweringPrepare - Added CIR-BEFORE-LPP checks
✅ Add -O1 RUN line for CIR output - Added CIR-O1 checks

Ready for re-review.

https://github.com/llvm/llvm-project/pull/171915