* [codegen] add encodings for iadd carry variants
Add encodings for iadd carry variants (iadd_cout, iadd_cin, iadd_carry)
for x86_32, enabling the legalization for iadd.i64 to work.
* [codegen] remove support for iadd carry variants on riscv
Previously, the carry variants of iadd (iadd_cin, iadd_cout and
iadd_carry) were being legalized for isa/riscv since RISC architectures
lack a flags register.
This forced us to return and accept booleans for these operations, which
proved to be problematic and inconvenient, especially for x86.
This commit removes support for said statements and all dependent
statements for isa/riscv so that we can work on a better legalization
strategy in the future.
* [codegen] change operand type from bool to iflag for iadd carry variants
The type of the carry operands for the carry variants of the iadd
instruction (iadd_cin, iadd_cout, iadd_carry) was bool for compatibility
reasons for isa/riscv. Since support for these instructions on RISC
architectures has been temporarily suspended, we can safely change the
type to iflags.
