YCM does not work out of a box for Ubuntu 12.04

Starting Vim with freshly installed YCM fails with:

```
Error importing ycm_core. Are you sure you have placed a version 3.2+ libclang.[so|dll|dylib] in folder... /home/rjeczalik/.vim/bundle/YouCompleteMe/autoload/../python/ycm_core.so: undefined symbol: clock_gettime
```

I've attached a diff to link it additionally with librt.