review(S): 7042153: guarantee(x_compare_res != Constant::not_comparable) failed: incomparable constants in IfOp

[Igor Veresov]

In C1, during IfOp elimination we can try to fold and IfOp that has 
constant objects as an arguments to the condition that are unloaded (not 
known at compile time) and are going to be patched later.
The solution is to check for such cases in make_ifop().

Webrev: http://cr.openjdk.java.net/~iveresov/7042153/webrev.00/

Tested with a short testcase, which I added to the regression suite.

Thanks,
igor