Originally, for each non-deleted instruction, CfgNode::emit() would call the virtual Inst::emit() and then print a newline (also printing end-of-live-range info as necessary).  This resulted in clumsy blank lines in the asm output, corresponding to non target specific pseudo instructions such as FakeDef, FakeUse, FakeKill.

We change this so that CfgNode::emit() only prints a newline for an InstTarget subclass, or if any end-of-live-range text was printed.

If a high-level instruction still wants to emit something in a comment, it's responsible for printing its own newline.

BUG= none
TEST= ./pydir/szbuild_spec2k.py -O2 --force -v --filetype=asm --sz=--asm-verbose=0
TEST= ./pydir/szbuild_spec2k.py -O2 --force -v --filetype=asm --sz=--asm-verbose=1
TEST= ./pydir/szbuild_spec2k.py -O2 --force -v --filetype=asm --target=arm32
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1431353003 .