[PATCH 34/79] [Backport to 15][DebugInfo] Support multiple CompileUnits (#1950)

[PATCH 34/79] [Backport to 15][DebugInfo] Support multiple CompileUnits (#1950)

It's possible for LLVM IR module to contain multiple CU in case if this module is a result
of llvm-link between two modules compiled for different languages and or compiled with
different options.

This patch introduces handling of such modules.
std::unordered_map<SPIRVId, std::unique_ptr> BuilderMap was introduced
to SPIR-V consumption part and
std::unordered_map<const DICompileUnit *, SPIRVExtInst *> SPIRVCUMap was introduced
to SPIR-V generation part to preserve Scope relations between DI metadata in SPIR-V and vice versa.

Note, that DIBuilder has a single CU field and this class is not trivially copiable.

Signed-off-by: Sidorov, Dmitry <dmitry.sidorov@intel.com>
Gbp-Pq: Name 0034-Backport-to-15-DebugInfo-Support-multiple-CompileUni.patch