[clang] [llvm] [clang][OMPIRBuilder] Use default target AS to create types (PR #158152)

[Tom Eccles via llvm-commits]

https://github.com/tblah approved this pull request.

The changes LGTM thanks.

if you are trying to enable SPIR-V more generally, you will also need to set this in `mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp` to fix the other upstream user of OMPIRBuilder. There are already code examples in that file showing how to fetch the default address space from the data layout string in the MILR module. 

https://github.com/llvm/llvm-project/pull/158152