PointerType and VPtrType have hard-coded sizes and alignments of 64/8
bits. On targets with 32-bit pointers (e.g., nvptx, spirv32), this trips
the record layout builder. Any record containing a pointer hit the
insertPadding assertion (offset >= size)
because the pointer was sized at 8 bytes while the following field was
placed at the AST-mandated 4-byte offset.
### Changes:
- CIRGenerator: attaches a CIR-native cir.ptr data-layout entry at
module setup, storing {size-in-bits, abi-align-in-bits} read
from the target DataLayout (only for the default address space).
- CIRTypes: PointerType reads its size/alignment from that entry
(falling back to 64/8 when absent); VPtrType routes through a cir.ptr so
it picks up the same width.
- LowerToLLVM: strips the cir.ptr entry during CIR→LLVM lowering, since
cir.ptr has no meaning in LLVM IR.
- Unit test: checking 4-byte pointer/vptr layout on nvptx, verified
across CIR, CIR→LLVM.
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