This change adds implementation for named barriers for SPIRV backend.
Since there is no built in API/intrinsics for named barrier in SPIRV,
the implementation loosely follows implementation for AMD
### Issue: Dimension override missing
When variable count expressions were used with stride, the constant
subsection path computed size first. This marked `ArgSizes` with byte
size semantics. Variable expression logic later triggered, but reused
`ArgSizes` assuming "bytes" semantics
`OMPIRBuilder.cpp` didn't handle dimension count for
`OMP_MAP_NON_CONTIG` flag
**Result**: `ArgSizes` wasn't overwritten with dimension count, breaking
non-contiguous mapping.
**Fixes**:
`llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp` - Expression semantics for
non-contiguous.
stride/count.
Generate 3D descriptor structures with runtime dimensions.
Fix dimension override to use dimension count instead of byte size.
Added testcases to cover stack arrays, heap pointers, struct members,
etc.
