It is very convenient for pipeline trace viewing to differentiate
  between compiler NOPs and pipeline bubbles.

We now split out the spike executable into another subproject,
which depends on both rocket and hwacha

They really aren't independent libraries.

Conflicts:
	hwacha/hwacha.mk.in

Surprising we got away without doing this for so long

We now use a heavily unrolled loop as the software I$, which allows the
host machine's branch target prediction to associate target PCs with
unique-ish host PCs.