try to fix the ARM self host bots
try to fix the ARM self host bots

The default target is ARM on the ARM self host bots.  This is problematic since
the behaviour on x86, x64 is different from ARM.  Explicitly pass the target.
This should hopefully fix the ARM bots.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@249229 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,apple/swift-clang,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,apple/swift-clang,apple/swift-clang