Driver: Fix a number of -fapple-kext issues:

 - Disable RTTI.
 - Disable use of __cxa_atexit.
 - Disable unwind tables.
 - Enable freestanding mode.

Also, honor -fhosted correctly.

<rdar://problem/7515383> C++ support: -fapple-kext not honored

llvm-svn: 99041