[clang][OMPIRBuilder] Use default target AS to create types (#158152)
Currently we assume that `0` is the default AS, which is usually true,
but it isn't for `SPIR-V`.
Pass down the AS from `clang` and use it to create types.
After this change, we finally generate fully valid SPIR-V for a basic
OpenMP Offloading example.
Signed-off-by: Sarnie, Nick <nick.sarnie@intel.com>