The -fapple-kext flag was designed to "do the right thing" for building code for

use in KEXTs. However, users/Xcode still need to tweak the linker flags to do 
the right thing, and end up using -Xlinker, for example.  Instead, have the 
driver "do the right thing" when linking when -fapple-kext is present on the 
command line, and we should have Xcode use -fapple-kext instead of setting other
flags like -Xlinker -kext or -nodefaultlibs.
rdar://7809940

llvm-svn: 136294