RFR(L): 8203197: C2: consider all paths in loop body for loop predication

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8203197/webrev.01/

Incremental change:

http://cr.openjdk.java.net/~roland/8203197/webrev.00-01/

The new webrev doesn't include the MDO change anymore as it was pushed
under a separate CR. I fixed the issues that Nils reported as well.

Also, to properly leverage the MDO change, I realized that the previous
patch was not sufficient: ideally we would want a profile_predicate trap
to be recorded in the header of an existing profile data entry but there
might not be one where the predicates are added (in the loop
header). To work around that problem, the new patch tries to add the
predicates at a if that dominates the loop header.

Roland.