Replace -fobjc-default-synthesize-properties with disable-objc-default-synthesize-properties.

We want the modern behavior most of the time, so inverting the option simplifies
the driver and the tests.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191551 91177308-0d34-0410-b5e6-96231b3b80d8