Force i[0-9]86 to i386 when using LLVM_HOSTTRIPLE.
Force i[0-9]86 to i386 when using LLVM_HOSTTRIPLE.

Only use major part of OS version when on darwin and modifying OS part
of target triple.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@60957 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang