This PR generation of argument types of internal intrinsic functions
`spv_const_composite` and `spv_track_constant`, so that composite
constants of ConstantVector type preserve their correct type in
transformation passes and can be successfully used further by LLVM
intrinsic functions.
The added test case serves two purposes: it is to check the above
mentioned fix and to demonstrate that a call to __builtin_alloca() maps
to instructions from SPV_INTEL_variable_length_array when this extension
is available.
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