Simplify the dead EBB argument tracking.
Simplify the dead EBB argument tracking.

It is not necessary to to a second pass over the live values to update
the set of available registers. The color_args() and color_entry_args()
functions can do that in a single pass.

sunfishcode/cretonne,stoklund/cretonne,sunfishcode/cretonne,stoklund/cretonne,sunfishcode/cretonne,stoklund/cretonne