API for querying which specialization constants exist.
To modify a specialization constant before compile(), use get_constant(constant.id),
then update constants directly in the SPIRConstant data structure.
For composite types, the subconstants can be iterated over and modified.
constant_type is the SPIRType for the specialization constant,
which can be queried to determine which fields in the unions should be poked at.
API for querying which specialization constants exist. To modify a specialization constant before compile(), use get_constant(constant.id), then update constants directly in the SPIRConstant data structure. For composite types, the subconstants can be iterated over and modified. constant_type is the SPIRType for the specialization constant, which can be queried to determine which fields in the unions should be poked at.