Color EBB arguments.

When coloring registers for a branch instruction, also make sure that
the values passed as EBB arguments are in the registers expected by the
EBB.

The first time a branch to an EBB is processed, assign the EBB arguments
to the registers where the branch arguments already reside so no
regmoves are needed.

lib/cretonne/src/ir/valueloc.rs

@@ -8,7 +8,7 @@ use ir::StackSlot;
 use std::fmt;
 
 /// Value location.
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum ValueLoc {
     /// This value has not been assigned to a location yet.
     Unassigned,