Legalize function call signatures.

SPIR-V calling convention does not allow passing struct types by value.
The SPIR-V adaptor handles this by converting struct arguments and return value to be pass-by-pointer.

New pass added: LegalizeFunctionSignatures
- Follows SPIR-V calling convention for struct types, but extends this to other APIs that does not use SPIR-V path.
- Arrays are also converted to pass-by-pointer.
- Illegal integer vector sizes are upscaled to legal integer types.
- In order to reduce BE complexity for stack calls, return on stack functionality will be removed. This pass will convert all return types > 64 bits to a pass-by-pointer argument.

Change-Id: Ib52507a616146d0cba65ef349f5e89f0448f09f9

Author: dlei6g