Make -findirect-virtual-calls and -fterminated-vtables aliases of -fapple-kext.

Make -findirect-virtual-calls and -fterminated-vtables aliases of -fapple-kext.
Outside the driver, they were already treated that way, but the driver was not
giving them the same special treatment as -fapple-kext, e.g., falling back to
llvm-gcc for i386/Darwin kexts.  Radar 9868422.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137639 91177308-0d34-0410-b5e6-96231b3b80d8