[C-extension] Generate C-extension instructions in macro-assembler

[penguinwu]

For each C-extension instruction, such as load/store or arithmetic operations, try to create a corresponding macro-assembler API (if not already existing) that would generate C-extension instructions when target architecture supports C extension and that the registers/offsets of the API satisfy the constraints of C-extension instructions.

For instance, existing TurboAssembler::Add(...) can be extended to generate C.ADDI, C.ADDIW, and C.ADDI16SP.

Please breakdown the support into separate issues so that they can be reviewed thoroughly (as there is not a clear definition which macro-assembler APIs may generate C extension instructions)

• Stack-pointer-based loads and stores
• Register-based loads and stores
• Control transfer
• Integer Constant-Generation
• Integer Register-Immediate Operations
• Nop, break

[lazyparser]

Hi @derekztu22

Are you still working on this task, or would you mind if I close/reassign?