llvm-spirv does not output optional literals in OpExecutionMode

[ex-rzr]

When Execution Mode is SubgroupsPerWorkgroup (36) it outputs
4 ExecutionMode 4 36
It should output: 4 ExecutionMode 4 36 <integer literal>.
I haven't try all other Execution Modes, but it works correctly for LocalSize, LocalSizeHint, VecTypeHint.

(spirv-dis from SPIRV-Tools shows “OpExecutionMode %4 SubgroupsPerWorkgroup 12” as expected)

[AlexeySotkin]

Possibly will be fixed in the new repo by switching to SPIRV-Tools format