[Refactor] TAddNode.Simplify rearranging

Summary

This merge request seeks to simplify some of the optimisations in taddnode.simplify by detecting whether one of the operands is an integer constant and ensuring it is always on the right-hand side for a commutative operation (i.e. addition, multiplication, bitwise AND, bitwise OR and bitwise XOR, but not subtraction). This results in the removal of duplicate code and hence increased maintainability.

System

• Processor architecture: All

Relevant logs and/or screenshots

There are a couple of noted cases where the generated code is slightly different, one in dateutils and one in zdeflate. In the case of zdeflate, the register allocator switches some registers around. For dateutils, some code executes in a different order, but the end result is the same - before:

.section .text.n_dateutils_$$_datetimetojuliandate$tdatetime$$double,"ax"
	...
	subl	$3,%eax
	addl	%edx,%eax
	movslq	%ecx,%rcx	; ---- BLOCK 1 START ----
	movq	%rcx,%r8
	movq	%rcx,%rdx
	sarq	$63,%rdx
	andq	$3,%rdx
	addq	%rdx,%r8
	sarq	$2,%r8		; ---- BLOCK 1 END----
	cltq			; ---- BLOCK 2 START ----
	imulq	$153,%rax
	leaq	2(%rax),%r9
	movq	$7378697629483820647,%rax
	imulq	%r9
	sarq	$1,%rdx
	shrq	$63,%r9
	addq	%r9,%rdx
	movzwl	32(%rsp),%eax
	addq	%rdx,%rax
	imulq	$365,%rcx,%rdx
	addq	%rdx,%rax	; ---- BLOCK 2 END----
	leaq	(%r8,%rax),%r9
	...

After:

.section .text.n_dateutils_$$_datetimetojuliandate$tdatetime$$double,"ax"
	...
	subl	$3,%eax
	addl	%edx,%eax
	cltq			; ---- BLOCK 2 START----
	imulq	$153,%rax
	leaq	2(%rax),%r8
	movq	$7378697629483820647,%rax
	imulq	%r8
	sarq	$1,%rdx
	shrq	$63,%r8
	addq	%r8,%rdx
	movzwl	32(%rsp),%eax
	addq	%rdx,%rax
	movslq	%ecx,%rcx	; ---- BLOCK 1 START---- (crossover start)
	imulq	$365,%rcx,%rdx
	leaq	(%rax,%rdx),%r8	; ---- BLOCK 2 END---- (crossover end)
	movq	%rcx,%rax
	movq	%rcx,%rdx
	sarq	$63,%rdx
	andq	$3,%rdx
	addq	%rdx,%rax
	sarq	$2,%rax		; ---- BLOCK 1 END----
	leaq	(%r8,%rax),%r9
	...

Additional notes

• With the dateutils example, there is no chance of side-effects because one of the operands has to be an integer constant for the node branch swap to take place, so if the other node is a function call, for example, it cannot affect the outcome.
• Under x86_64-win64, -O4, the compiler is 512 bytes smaller.