…nce (#2736)

This PR partially fixes issue #2702 in the part that is responsible for SPIR-V to LLVM IR translation. Namely, this PR ensures that all PHI nodes of a Function has the number of incoming blocks matching block's predecessor count. When a PHI node doesn't conform to this rule, this PR inserts missing number of (Value, Basic Block) pairs to make the PHI node valid.

Another problem from #2702, that is violation of the requirement to OpPhi's to have exactly one Parent ID operand for each parent block of the current block in the CFG in the output SPIR-V code, is out of scope of this PR.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@7d7f946dbd51236