[darwin] [builtins] Stop generating cc_kext_ios5 and move iOS architectures...

[darwin] [builtins] Stop generating cc_kext_ios5 and move iOS architectures out of cc_kext into cc_kext_ios

Summary:
Xcode 7 doesn't support targeting iOS5 and earlier. Instead of just dropping cc_kext_ios5, I've repurposed it to cc_kext_ios, and I'm pulling the iOS architectures out of cc_kext. Putting OS X and iOS slices inside the same archive was just odd.

There is a cooresponding clang change coming too.

Reviewers: bogner, bob.wilson

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13112

llvm-svn: 248441