New size optimization

[Jim Wilson]

I was talking to Anthony Green about this, and he mentioned that it might be
useful to add a flag to disable loop-invariant-code-motion and then have -Os
set that flag.  That is, we perhaps should make -Os work like -O2.  -O2 just
sets a bunch of flags, and the user can override the choices if they are wrong
for a particular application.  We should perhaps do the same for -Os, making
it set a bunch of flags that the user can override if the defaults weren't the
best possible choice.  There is a tradeoff with having too many -f options
that the user gets confused though.

Is there any reason why you just disabled the last part of the LICM code, and
not all of it?  Maybe strength reduction needs some of the info computed by
LICM.  Or maybe you didn't try disabling the rest of it?  It is probably useful
to document why this choice was made in a comment.

Jim