RFR(S) 8185134: Introduce vm.graal predicate

[Ekaterina Pavlova]

Hi all,

could you please review this small change which introduces vm.graal.enabled predicate
and marks compiler tests which fail with Graal due to c2 specific checks by '@requires !vm.graal.enabled'.

     bug: https://bugs.openjdk.java.net/browse/JDK-8185134
  webrev: http://cr.openjdk.java.net/~epavlova//8185134_test/
          http://cr.openjdk.java.net/~epavlova//8185134_hs/


Tested by running failing tests in Graal as JIT compiler mode
(-XX:+TieredCompilation -XX:+UseJVMCICompiler -Djvmci.Compiler=graal).

thanks,
-katya

p.s.
  Igor Ignatyev volunteered to sponsor this change.