Improved inline multiplication in JIT for x86

[potatosalad]

This moves multiplication for small integers inline with overflow checking, along with specialization for when the left or right hand side are immediates.

The original comments related to clobbering RDX, I think, are incorrect based on how we're using imul in 2-operand form instead of 1-operand form (see reference docs for imul):

We avoid using ARG2 and ARG3 because multiplication clobbers RDX, which is
ARG2 on Windows and ARG3 on SystemV.

As a very non-scientific benchmark: based on some tests involving a pure Erlang version of MurmurHash3_x86_32 with a 1MB input key, this change alone roughly doubled performance for me (30ms originally down to 15ms).

[CLAassistant]

All committers have signed the CLA.

[garazdawi]

Thanks!