RFR: missing UseShenandoahGC checks in 9

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/shenandoah/9_useshenandoahgc/webrev.00/

Same as with 8u. 

FYI, I see failures with gc/shenandoah/compiler/TestReferenceCAS.java
when ran with -Xcomp (reproducible with and without this patch):

Error occurred during initialization of boot layer
java.lang.InternalError: BMH.reinvoke=Lambda(a0:L/SpeciesData<LLL>,a1:L,a2:L,a3:L,a4:L,a5:L,a6:L)=>{
    t7:L=BoundMethodHandle$Species_L3.argL2(a0:L);
    t8:L=MethodHandle.invokeBasic(t7:L,a5:L);
    t9:L=BoundMethodHandle$Species_L3.argL1(a0:L);
    t10:L=MethodHandle.invokeBasic(t9:L,a4:L);
    t11:L=BoundMethodHandle$Species_L3.argL0(a0:L);
    t12:L=MethodHandle.invokeBasic(t11:L,a1:L,a2:L,a3:L,t10:L,t8:L,a6:L);t12:L}
Caused by: java.lang.ArrayIndexOutOfBoundsException: -1

And also NPEs sometimes. 

I also saw those failures with 10 at some point but couldn't reproduce
them later.

Roland.