Make test/Driver/darwin-sdk-version.c pass on hosts < macOS10.14
Make test/Driver/darwin-sdk-version.c pass on hosts < macOS10.14

The test test/Driver/darwin-sdk-version.c from r349380 checks if the macOS
deployment target can be correctly inferred from the SDK version. When the
SDK version is > host version, the driver will pick the host version, so
the old test failed on macOS < 10.14. This commit makes this test more
resilient by using an older SDK version.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@349393 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 6138c88ecafacb940701524001d2ae88bb8c3cf1)

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang