[OSX]building fails: symbol(s) not found for architecture x86_64

Fail when build following the merge of dotnet/coreclr#117 :

```
Undefined symbols for architecture x86_64:
ld: symbol(s) not found for architecture x86_64
make: *** [all] Error 2
Failed to build coreclr components
```

full error log: https://gist.github.com/cnblogs-dudu/b314a28943bb365c4077
But building `git clone -b osx --single-branch https://github.com/kangaroo/coreclr.git` is ok.
