Bump sanitizer iOS deployment target to 9.0

Bump default value for `-miphoneos-version-min=x` to 9.0 (from 8.0).
TSan tests that use thread local storage `__thread` (e.g., tls_race.cpp)
are failing to link for the iOS simulator (arch=x86_64 and
-miphoneos-version-min=8.0) on internal/master (will be submitted to
Glacier train):
```
ld: targeted OS version does not support use of thread local variables in _main for architecture x86_64
```

iOS 9.0 was released 2015.