Write a more efficient branch-less version

[todo]

Pyjion/src/pyjion/pycomp.cpp

Lines 2599 to 2604 in 20e3b04

	// TODO : Write a more efficient branch-less version
	Label is_positive = emit_define_label();
	m_il.dup();
	m_il.ld_r8(0.0);
	emit_branch(BranchGreaterThanEqual, is_positive);
	m_il.neg();

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This issue was generated by todo based on a TODO comment in 20e3b04 when #427 was merged. cc @tonybaloney.