[14] RFR (S) 8236000: VM build without C2 fails

[Vladimir Kozlov]

https://cr.openjdk.java.net/~kvn/8236000/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8236000

C2 flags should be checked only when C2 is present. Running debug VM build with JVMCI but without C2 found other issues 
which were fixed too:

#  Internal Error (src/hotspot/share/jvmci/jvmci_globals.cpp:121), pid=2398, tid=2403
#  assert(MaxVectorSizechecked) failed: MaxVectorSize flag not checked

and

# Internal Error (src/hotspot/share/gc/serial/genMarkSweep.cpp:98), pid=10108, tid=10118
# assert(DerivedPointerTable::is_active()) failed: Sanity

Tested build with --with-jvm-features=-compiler2 and --with-jvm-features=-compiler2,-jvmci
and tier1.

Thanks,
Vladimir