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Added support for generation of unscaled immediate memory offsets.
Fixed compilation errors.
Modified calling of the c 'exit' function in tests so that it will expect a int<64> instead of an int<32>.
Modified formating of various IR things (like Value's and Instructions) to be more easillly readable.

This reverts commit 54ce8e1c.

1. compiler knows all the registers
2. but only 64bits register is a color (for reg alloc)
3. backend records the length of GPR for each operand during instruction
selection
4. after reg alloc, when replacing temp with a color, find corresponding
GPR for the length recorded before

Note: made two places in api implementation as unimplemented as
the instruction/type chnaged.