Issue Description:

Xcode 8 Beta
OS: 10.11.5

1. Install Swift Toolchain https://swift.org/builds/development/xcode/swift-DEVELOPMENT-SNAPSHOT-2016-06-20-a/swift-DEVELOPMENT-SNAPSHOT-2016-06-20-a-osx.pkg
2. Select the new toolchain
3. Create a new iOS single view project
4. Build the project.

```
<unknown>:0: error: invalid version number in '-miphoneos-version-min=10.0.0'
Assertion failed: (Maj < 10 && Min < 100 && Rev < 100 && "Invalid version!"), function getDarwinDefines, file /Users/buildnode/jenkins/workspace/oss-swift-package-osx/llvm/tools/clang/lib/Basic/Targets.cpp, line 158.
0 swift 0x000000010568a00b llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 43
1 swift 0x0000000105689256 llvm::sys::RunSignalHandlers() + 70
2 swift 0x000000010568a75f SignalHandler(int) + 383
3 libsystem_platform.dylib 0x00007fff9c67752a _sigtramp + 26
4 swift 0x0000000106277599 cmark_strbuf__initbuf + 73928
5 swift 0x000000010568a4ae abort + 14
6 swift 0x000000010568a491 __assert_rtn + 81
7 swift 0x000000010571323f (anonymous namespace)::getDarwinDefines(clang::MacroBuilder&, clang::LangOptions const&, llvm::Triple const&, llvm::StringRef&, clang::VersionTuple&) + 6319
8 swift 0x00000001037c4884 InitializePredefinedMacros(clang::TargetInfo const&, clang::LangOptions const&, clang::FrontendOptions const&, clang::MacroBuilder&) + 53252
9 swift 0x00000001037b3221 clang::InitializePreprocessor(clang::Preprocessor&, clang::PreprocessorOptions const&, clang::PCHContainerReader const&, clang::FrontendOptions const&) + 449
10 swift 0x0000000103761547 clang::CompilerInstance::createPreprocessor(clang::TranslationUnitKind) + 1975
11 swift 0x00000001037979bb clang::FrontendAction::BeginSourceFile(clang::CompilerInstance&, clang::FrontendInputFile const&) + 3227
12 swift 0x00000001030736ed swift::ClangImporter::create(swift::ASTContext&, swift::ClangImporterOptions const&, swift::DependencyTracker*) + 11693
13 swift 0x0000000102f0686d swift::CompilerInstance::setup(swift::CompilerInvocation const&) + 813
14 swift 0x0000000102a20247 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2807
15 swift 0x00000001029e2de0 main + 2448
16 libdyld.dylib 0x00007fff9ccb25ad start + 1
17 libdyld.dylib 0x000000000000003d start + 1664408209
```