be: Factorise code to get the register Projs of the backend start nodes.
ia32: Avoid creation of duplicate Projs at the Start node.

Duplicate Projs are a problem when CSE is off, e.g. -O0.
amd64: Avoid creation of duplicate Projs at the Start node.

Duplicate Projs are a problem when CSE is off, e.g. -O0.
amd64: Lea alters neither flags nor memory.
amd64: Do not needlessly swap base and index of Lea.
amd64: Simplify condition calculation.
ia32: Simplify condition calculation.
lower: Simplify and comment is_equality_cmp().
irnode: Constify and reduce scope.